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Assessing PLA Underground Air Basing Capability

Air Power Australia Analysis 2011-01
  16th February 2011

A Monograph by
Sean O'Connor, BA, MS (AMU)
Dr Carlo Kopp, SMAIAA, SMIEEE, PEng
Text © 2011 Sean O'Connor, Carlo Kopp


PLA-AF Shenyang J-8 Finback fighters being towed into one of the PLA's many “super-hardened” underground air bases. Tunnelled horizontally into the sides of hills, these bases are unusually difficult to destroy and permit concealed preparations for operation, as fuelling, weapons loading and runup activity is invisible to orbital and airborne ISR assets. Note the open exterior blast door (Chinese Internet).

Abstract


The PLA's network of around forty underground airbases provides a unique and indeed superlative capability to withstand a large scale counter-air campaign, as significant effort with penetrating munitions of large mass would be required to close such bases down for the duration of the campaign, or permanently render them unusable.

As these bases deny surveillance by orbital, airborne or ground based ISR assets, they provide an inherent capability to perform covert preparations for combat operations, be it in times of conflict, or in the period immediately preceding a conflict.

The hangaring capacity of these underground bases is of the order of at least 1,500 combat aircraft, possibly greater,  if more than basic internal tunnel arrangements have been employed.  This capacity represents more than the total number of modern combat aircraft currently operated by the PLA.

In strategic terms, the PLA's underground airbase infrastructure provides a capability to deny  at this time even the United States the opportunity to inflict massive early attrition upon the PLA's fleet of combat aircraft, while these are on the ground. This would force any opponent, including the United States, into a protracted aerial war of attrition, before decisive losses could be inflicted upon the PLA combat aircraft fleet.

The inherent survivability of the PLA's impressive underground airbase infrastructure has not been a major consideration in the ongoing debate in the United States on the utility, and indeed intended design, of the replacement heavy bomber aircraft. If the defeat of the PLA's underground airbase infrastructure is part of the intended role of this future aircraft, then this aircraft will need to combine the survivability needed to repeatedly penetrate what is becoming the most capable Integrated Air Defence System in existence, with the ability to deliver heavy “earthquake bombs”. Anything less will result in unsustainable combat attrition.



Introduction


A unique feature of China's air power basing environment, compared to other major air forces, is the widespread use of underground or “super-hardened” hangars, of which more than forty have been identified from open source and declassified KH series reconnaissance satellite imagery.

Intended to maximise the survivability of aircraft and critical operational infrastructure under air attack, underground hangars have historically been used mostly by smaller air forces, such as those in Sweden, Switzerland, the DPRK, the former Yugoslavia, and the former socialist Albania. The motivation, typically, was to survive in a threat environment where the defending air force was numerically, and often, also technologically uncompetitive against the threat.

Deeply buried infrastructure, such as production and maintenance facilities, proved highly survivable during the Second World War, when Germany constructed a myriad of underground production lines, for critical material including A-4 ballistic missiles and fighter aircraft. These facilities proved highly resistant to carpet bombing using standard unguided munitions. The handful of successful attacks on similar underground targets involved exclusively the Royal Air Force 617 SQN, dropping Tallboy or Grand Slam “earthquake bombs”1.


Saumar Tunnel after attack by earthquake bombs in 1944 (RAF).

The advent of nuclear weapons in 1945, airburst at low or medium altitudes, produced considerable interest in hardened shelters and underground hangars during the late 1940s and 1950s, as the West and the Warsaw Pact expanded their nuclear warstocks and adapted their doctrine.

Aircraft parked on tarmacs, in WW2 style revetments, or on pads with earthwork berms, were vulnerable to nuclear blast overpressures, involving both direct pressure loading, or lifting and overturning by the passing shock transient. Glasstone documents several examples of structural damage from overpressure effects2.

Glasstone states that blast overpressure transients of 1 to 2 psi produce damage to exposed aircraft. Higher overpressures, typically from 4 to 10 psi, resulting from higher weapon yields or closer proximity to the epicentre,  will typically produce damage beyond economical repair.

Thermal radiation from nuclear blasts would have a limited effect on unpainted anodised aluminium aircraft skins due to the high infrared reflectance of aluminium, but is capable of igniting painted components and other airframe materials, as well as fuels. Glasstone details radiant intensities for 24 kiloton, 1.4 megaton and 20 megaton airbursts in Table 7.40.

Initial gamma radiation and neutron flux for early weapons presented primarily a threat to personnel, while bomb residue and other fallout could render aircraft and equipment unsafe for use.

Underground hangars therefore provided a very robust passive defence against nuclear blast, thermal and gamma radiation, electromagnetic pulse (EMP) effects and neutron flux, while permitting the whole operational servicing, refuelling and loading area, and aircraft storage to be protected from fallout. Protection against fallout in turn presented the opportunity to also protect the aircraft and personnel from exposure to biological and chemical weapons, both of which were widely deployed for operational use during that period.

While the primary imperative behind underground hangar designs was protection of aircraft, personnel, POL, munitions warstocks and support equipment against conventional bombing, nuclear bombing, and chemical  and/or biological agent deliveries, they presented another important advantage.

Underground hangars provide a measure of covertness absent in conventional basing, as operational activity can only be established once aircraft roll out of the caverns to depart on sorties. Fuelling, servicing, loading, testing and other activities can be conducted out the sight of airborne, orbital and surface observers.

The use of underground hangars is not without disadvantages. Unless a naturally occuring cavern is expanded or modified, the cost of tunnelling can be considerable, especially if the rock is of a hard igneous type, rather than soft sedimentary type. While the former offers much better protection than the latter, availability depends wholly on the local geology available.

Other unique and ongoing maintenance issues exist. One is ensuring that water does not penetrate or accumulate inside the tunnels. Trees growing near entrances or other surface features may damage the rock or concrete through root penetration. Vermin, such as birds and bats may seek shelter or nesting inside the tunnels, presenting a risk of contagion, but also presenting the potential for damage to equipment by FOD (swallowed stones) or corrosive guano.

China started constructing underground hangars as part of its large scale 1950s airfield construction effort, and declassified KH-4 Corona IMINT collected in 1962 - 1963 shows construction of such basing well under way at that time, including auxiliary alert runways and/or taxiways now known to lead to the hangar entrances.

CHINAUGFALL

China's Underground Airbases, Geographical Placement (red - PLAAF, blue - PLANAF, green - unidentified tenant afiliation) [Click to enlarge][KMZ Download].



KH-4 Corona wet film imagery of Chanzing AB in Nanjing MR, collected 1962-1963, showing underground hangar access under construction (US DoD via FAS).

A number of PLA airbases explored more recently using high resolution Google Earth IMINT indicate that some bases were specifically sited with the intent to construct underground hangars, which may have been commenced but was not completed. On other sites there is evidence of construction work on taxiways or hangar entrances, suggesting ongoing maintenance or construction effort. Some sites, such as the well known PLANAF base at Lingshui on Hainan Island, are optimally located next to a suitably large hill, but there is no evidence of underground hangar construction or associated taxiways, which does not preclude the construction of an underground hangar at a future date.

At this time a small number of the PLA's underground hangars are derelict, typically as a result of the associated airfield being converted to other than military operational use. Examples include the abandoned Daishan Island fighter base, south of Shanghai, and the completely overbuilt Yidu fighter base, converted to a warehousing area. Suburban encroachment appears to be the primary cause of PLA airfields being abandoned, although many have also been converted in recent years to civilian airports, often retaining some military use.

Most of the PLA's underground hangars appear to be in operational use at this time.

China's most prominent Cold War period client states, Albania and the DPRK, both constructed airbases with underground hangars patterned on the PLA design.


PLA Airbase Design Strategy, Base Construction and Capacity



The study of well in excess of 200 Chinese military, civil and dual use airfields shows a disciplined and highly standardised approach to airfield construction, with often identical runway, taxiway and tarmac arrangements for given categories of airfield.

Broadly, all designs observed revolve around three basic configurations, one for fighter bases, one for bomber bases, and one for transport bases, with the caveats that some bomber bases started life as fighter bases, and many transport, bomber and fighter bases have over the last decade been rebuilt into civil airports, which often retain a dual-use capability.

As late entrants in the game of military airfield construction, the Chinese had the benefit of extensive overseas experience, and most military airfields are patterned on standard and very robust Warsaw Pact fighter base designs of the 1950s period. There can be no doubt that Warsaw Pact engineers, especially Soviet engineers, played a pivotal role in establishing the PLA's airfield construction program during the 1950s.

Good comparative examples of construction are the former Soviet Frontal Aviation bases in Eastern Germany, such as Grossenhein, Templin-Gross, Altenburg-Nobitz, Tutow-Demin, Brand, Welzow, Damgarten, Wittstock, Eberswalde-Finow, ZerbstHinsterwalde, Juterbog, Merseburg, Rechlin and Sperenberg.



PLA AF Quzhou AB in the Nanjing MR.  Quzhou is atypical insofar as the revetments in the dispersal area are connected by a full arc of taxiway, requiring multiple 'cuts' by an attacker to close the taxiway. The revetment pads of typical PLA airfields are 75 to 100 ft in diameter and can accommodate up to three Farmer, Fantan or Fishbed fighters. or one or two Flankers. Dispersal taxiways are typically 45 ft wide. At least one Badger base has pads sized to fit a single aircraft, but no berms were installed. The PLA's approach to the construction of semi-hardened and hardened basing closely follows the Soviet Cold War model (US DoD).

Given a highly standardised approach to airfield layout, typically employing a single primary runway with a parallel taxiway, the latter often usable as a redundant runway, the principal differences between PLA fighter bases are typically to be found in the dispersal area arrangements, and whether the base employs an underground hangar. Mostly, fighter bases with underground hangars do not employ networks of taxiways and dispersal revetments, although dual taxiways to the hangar system are common. Most bases have alert aprons at either end of the main runway.

The “classical” Warpac style bases are well hardened by the standards of the era predating PGMs, usually employing horseshoe shaped earthwork berms around individual dispersal pads, thus making these difficult targets for low altitude strafing, rocket and dive bombing attacks. This dispersal arrangement has been observed at fighter bases, H-5 Beagle bases, and H-6 Badger bases.

At this time the global availability of PGMs capable of often very precise steep trajectory attacks largely defeats the Warpac era dispersal scheme, as individual revetments can be hit, and the linear or looped taxiway arrangement can be easily cut with a modest number of rounds. While the latter problem can be cheaply corrected by adding additional taxiway paths, the use of revetments at this time provides benefit only in reducing fratricide from exploding and burning aircraft.



TAB-V Hardened Aircraft Shelters at Kadena AFB, Okinawa, are not designed to survive hits from bunker buster penetrating munitions. Most PLA HAS are similar in appearance to TAB-V shelters  (US Air Force image).



Hardened Aircraft Shelters at Suixi AB and Xiangshui Hsu AB (Google Earth).



A number of these “classical” Warpac style bases have been further hardened more recently by the addition of HAS, which appear to be modelled on the NATO/US  lightweight TAB-V (Theatre Air Base Vulnerability) shelters. More than often bases employing TAB-V style shelters include camouflage paint on taxiways and shelters, and show evidence of earth piled over the shelters for additional protection, usually overgrown with foliage. There is no evidence of substantive numbers of heavy high strength reinforced concrete shelters designed to defeat  concrete penetrating weapons like the BLU-109/B, BLU-116/B, BLU-118/B or GBU-39/B.

PLA fighter bases with underground hangars have been constructed where local geography permitted, and we can surmise that the construction of the softer “classical” Warpac style bases simply reflected the geographical unavailability of suitable mountains, hills or hillocks in areas where an airbase needed to be constructed.

An interesting geographical feature of much of the eastern seaboard of mainland China is that very flat areas are frequently punctuated by isolated hills or mountains, or short chains of same, and it is at such sites that the PLA constructed most of its underground hangars in the Shenyang, Beijing, Jinan, Nanjing and Guangzhou MRs.

The arrangement of the airfield proper and the underground hangars varies widely, and clearly the engineers designing these sites sought to exploit the local geography to every extent possible. A factor which clearly impacted the placement of runways relative to the hill concealing the hangar was the flatness of terrain in close proximity to the hill. As a result, while many such bases have the runways and aprons placed within a hundred metres of the hill, in some instances the distance is as great as kilometres, a major impediment in sustaining high sortie rates.

A very useful feature observed in a good number of these bases is the construction of an auxiliary takeoff only runway in place of one of the dedicated taxiways, or a full capacity second runway fully capable of recovering aircraft. These auxiliary runways have one end usually placed immediately at one of the underground hangar entrances, which has an apron at the entrance, or within a few hundred yards, to permit aircraft to taxi out, line up, and immediately roll into a takeoff. Upon returning from a sortie the aircraft would land on the main runway, and then taxi or be towed along the auxiliary runway or taxiways back to the underground hangar. Usually a paved pad or apron is also sited at the midpoint of the auxiliary runway, or taxiway between the runway and hangar, to permit takeoffs while aircraft are being returned to the hangar. These sites are easily identified as the auxiliary runway is much wider than a standard taxiway, and is straight unlike many taxiway sections.  At some sites, the auxiliary runway is in a state of disrepair, and at one site it is clearly overgrown with vegetation.

Auxiliary takeoff only runways are installed at Chifeng AB, Zunhua AB, Jinzhou Xiaolingzi AB, Yinchuan / Xincheng AB, Lihue AB, Anqing AB, Changzing AB, Daishan Island AB, Feidong AB, Guiyang AB, Taihe AB, Yiwu AB, Foluo Northeast AB, Jiyuan AB, Leng Shui Chi AB, Yaotian AB, Guodu AB, Jiyuan AB, and Luyang AB, which constitute around 50 percent of known bases with underground hangars. It is likely that bases without such runways and having long taxiways simply lacked suitably flat local terrain for second runway construction.

Taxiways into underground hangar entrances reflect the placement of the entrances, which are mostly situated at opposite sides of the hill being used, although a modest number have entrances on the same side, up to 200 m apart. Mostly two entrances are employed, and the taxiways fork in a Y pattern, following the contours of the base of the hill. A small number of sites employ one entrance, but Guiyang AB in Nanjing MR, and Yinchuan AB in Lanzhou MR, each have four entrances in a single hill.



J-6A Farmers (Chinese Internet).



Both the J-8 Finback and J-7 Fishbed are compatible with the “fighter-sized” underground hangars (Zhenguan Studio, © 2010 Air Power Australia).



A H-5 (Il-28) Beagle, developed as an analogue to the Canberra and B-66 medium bombers, on display in the Datangshan underground hangar (Zhenguan Studio, © 2010 Air Power Australia).



The Luyang / Ranghe-Zhen AB site is employed at this time in part as a mass storage site, and in part as a museum. It is unusual in that it combines
“MiG-sized” hangars, “Beagle-sized” hangars and one partially completed “Badger-sized” hangar. Above, interior view of the “Badger-sized” hangar, currently used to display early fighter aircraft . The incomplete “MiG-sized” tunnel may have been intended to connect to the remainder of the tunnel system (Chinese Internet).

Comparative entrance sizes for PLA underground hangars, scaled from imagery. Some fighter base entrances are as narrow as 12 metres, while some “Badger-sized” base entrances may be as wide as 40 metres. There are eight known  35 - 40 metre wide “Badger-sized” hangars, one of which is decommissioned, fourteen known ~22 metre wide “Beagle-sized” hangars, and seventeen known 12 to 14 metre wide “MiG-sized” hangars (C. Kopp).

Study of satellite imagery indicates that bases are constructed with three standard widths for the underground hangar entrances. If we assume these were planned around period PLA-AF/NAF combat aircraft, we observe the following:
  • “MiG-sized”: 12 - 15 metre entrance widths compatible with the J-4/MiG-15 Fagot, Q-5 Fantan,  J-5/MiG-17 Fresco, J-6/MiG-19 Farmer, J-7/MiG-21 Fishbed and later J-8 Finback;
  • “Beagle-sized”: ~22 metre entrance widths compatible with the H-5 Beagle;
  • “Badger-sized”: ~35 - 40 metre entrance widths compatible with the H-6 Badger.
The entrance width most commonly observed is ~45 ft (~14 m), evidently sized for legacy PLA fighter aircraft but still compatible with the more recent J-8 Finback and JH-7 Flounder. This explains why J-11A/B Flankers have not been observed operating from such hangars, as the Flankers' 48 ft 3 in (14.7 m) wingspan is simply too great to permit entry.

Operating the J-11A/B from these sites would require the retrofitting of the Su-27K/Su-33/J-15 folding wing, or manufacture of new aircraft with same, or excavation of the tunnel to a greater size.

The new Chengdu J-10A/S/B has a span of 31 ft 10 in (9.7 m) and will comfortably fit all PLA underground hangars.

The prototype Chengdu J-20 would require folding wings, or at least wingtips, to fit the 14 metre width entrances.

Many of the bases observed have ~22 metre width entrances, and evidently were constructed for H-5 Beagle units, the span of this aircraft being 21.5 metres. These could accommodate the J-11A/B, Su-30MKK/MK2 and the J-20 without modification of the aircraft or tunnels.

A half dozen of the known operational sites have 33 to 40 metre wide entrances, permitting access for the H-6 Badger, and thus compatible with all smaller types.



H-6 Badgers being towed from an underground hangar. Six of the known sites have 30 metre entrances permitting access for the H-6 Badger (Chinese Internet).


The Beijing Shahezhen AB site, better known as the Datangshan Museum, has an underground hangar sized for the Tupolev Tu-16 / Xian H-6 Badger. Datangshan is the only PLA underground hangar accessible to the general public.

Internal arrangements used in PLA underground hangars are mostly unknown, as very few images exist in the public domain. Given the nature of underground hangars, numerous possibilities exist in terms of internal layouts.

Importantly, most sites with underground hangars are devoid of external hangars which would in other basing be used for engineering work on aircraft.

Stowing fighter aircraft in underground hangars presents similar challenges to those seen in aircraft carrier hangar decks, but with the difference that hangar decks have width usually absent in underground hangars. The PLA will therefore have developed numerous procedures for aircraft handling in such confined spaces.



Significant increases in internal storage capacity and supporting capabilities such as materiel storage and personnel accommodation can be achieved by using complex rather than simple internal topologies (C. Kopp).

The simplest internal arrangement which is compatible with the entrance layouts of the known underground hangars is a simple straight, curved or segmented tunnel connecting the two entrances. This is indeed the arrangement at Datangshan, where the overall length of the hangar between the entrances is just over 500 metres. Assuming H-6 aircraft parked nose to tail, this site could accommodate at least a dozen aircraft, which is a standard PLA-AF squadron.

If we consider a simple straight, curved or segmented tunnel connecting the two entrances as the standard internal layout, the linear distance between the entrances provides a reasonable measure of internal capacity. For most of the sites, ~500 metres was measured, although some are up to 1,000 metres apart, and some as little as ~300 metres apart. Sites with same-side entrances will likely employ a horseshoe shaped loop4.

Annex B contains a preliminary and very conservative assessment of the capacity available in the PLA's network of underground hangars. This assessment does not consider the impact of additional branching tunnels, or forks and parallel tunnels, which could significantly expand capacity for aircraft and materiel. As such it may underestimate extant hangar capacity, and certainly underestimates the potential capacity, were the PLA to expand these hangars by additional enlargement of extant tunnels or further tunnelling.

The seven known operational “Badger-sized” underground hangars have a minimum capacity of the order of 120 H-6 aircraft, which suggests on currently cited H-6 numbers, that the whole PLA H-6 fleet could be accommodated.

The fourteen known “Beagle-sized” underground hangars have a minimum capacity of the order of 600 Flankers, or 500 J-20 aircraft. Again, this would accommodate all extant PLA Flankers with surplus capacity. Similar numbers of the JH-7 Flounder could be also accommodated.

The seventeen known “MiG-sized” underground hangars have a minimum capacity of the order of 600 to 800 J-10 Sino-canard fighters, which is a substantial fraction of the intended production numbers.

At least three more underground hangars are known, but given limitations in currently available imagery, capacity cannot be reliably assessed.

The aggregate number of combat aircraft which could be accommodated is at a minimum of the order of 1,500, considering that the highest value types would be placed into such hangars under conditions where attacks on the mainland were expected.


Underground Air Base Vulnerability



Of the available techniques for constructing hardened airfields, underground airbases are the least vulnerable to both conventional and nuclear weapons effects, and thus present as an attractive choice in a environment where precision guided munitions have proliferated globally. With pervasive orbital and airborne ISR capabilities, the concealment of operational preparations afforded by underground hangars is much more valuable than when these were initially constructed.

A detailed discussion of “bunker busting” free fall bomb and cruise missile warheads can be found in earlier publications3.

In summary, modern “bunker busting” weapons fall into several classes, with varying penetration performance,  employing conventional and more recently thermobaric explosive fillers. Refer Table 1.

Small Diameter Bombs Standard Penetrators Deep Penetrators Heavy Penetrators
GBU-39/B SDB I (385 lb)
BLU-109/B (2,000 lb) BLU-113/B (4,800 lb) GBU-57A MOP (30,000 lb)
Luoyang LS-6 (100 kg) BLU-116/B AUP (2,000 lb) BLU-122/B (4,800 lb)
Luoyang LS-6 (50 kg) BLU-118/B (2,000 lb) KAB-1500 (1,500 kg)

KAB-500 (500 kg)

Table 1.

Small Diameter Bombs
and Standard Penetrators were developed primarily to defeat Hardened Aircraft Shelters and other hardened surface structures, primarily built using steel reinforced high strength concrete. These weapons are known to penetrate 6 to 12 ft of reinforced concrete, subject to the concrete strength and delivery method. Such weapons are sized for internal or external carriage by fighters.

Deep Penetrators were developed primarily to defeat underground bunkers, and can penetrate up to 18 ft of reinforced concrete, or less under some depth of soil or soft rock. These weapons are sized for internal carriage by heavy bombers or external carriage by heavy strike fighters, such as the F-111, F-15E, or Flanker.

Heavy Penetrators were developed primarily to defeat deep underground bunkers, and represent a modern reimplementation of the 1940s “earthquake bomb” concept. They can only be lifted by heavy bombers, equipped with special adaptors. These weapons are intended to produce a high velocity shock wave in the rock which will collapse bunkers, tunnels or other deeper structures.



Earthquake Bombs Past and Current






RAF 617 SQN Lancaster dropping a Tallboy. The aircraft had numerous modifications applied to carry and target the demanding Tallboy and Grand Slam bombs, including a unique sculpted bomb bay (RAF).



Tallboy after release, prior to pitchover, and spin up (RAF).



12,000 lb Tallboy ground handling (RAF).



30,000 lb GBU-57A/B Massive Ordnance Penetrator, built for carriage by the B-1B, B-2A and B-52H (Boeing).





GBU-57A/B Massive Ordnance Penetrator release from a B-52H (DTRA).





Tactics for counter-air strikes on airfields today mostly reflect the Desert Storm model, but using contemporary aircraft and weapons. In Desert Storm, Coalition F-117A and F-111F aircraft dropped pairs of GBU-24/27/BLU-109B weapons on HAS, and GBU-10/Mk.84 on runways and taxiways, while RAF Tornados did much the same using GBU-10/Mk.84, with laser illumination provided by Tornado GR.1/TIALD or Buccaneer S.1/Pave Spike “master bombers”.

In a contemporary conflict, the delivery platforms of choice would be the F-22A Raptor armed with the penetrating GBU-39/B SDB and B-2A Spirit armed with the penetrating GBU-39/B SDB and/or deep penetrating GBU-31/B/BLU-116/B AUP, as only these aircraft types have the survivability to repeatedly penetrate a modern IADS without incurring unsustainable attrition.

These weapons and tactics would provide some effect against a base equipped with an underground hangar, but do not provide a high probability of a robust and unrecoverable kill.

In conventional steep terminal trajectories, these bomb types could be used to damage the hangar entrances and in some instances cause the entrance roof to cave in, or mountainside above the entrance to collapse. There is no guarantee that significant damage would be inflicted on aircraft and other materiel inside the hangar, presenting good odds that the site would be operational again in a day or so. Damage to runways and taxiways can be repaired quickly, if planned for.

The ability of these munitions to penetrate the rock in proximity to the hangar entrance, or above the hangar cavity, depends not only on the design and terminal trajectory of the munition, but also on the mechanical properties of the rock. Southern and Eastern China, where most underground hangars are situated, has an abundance of dense igneous rock formations,  many with high fracture toughness.

Where the weapon autopilot software permits a horizontal or very shallow terminal trajectory, and entrance placement permits, the weapon can be programmed to fly horizontally into the hangar entrance and initiate deep inside the hangar. This mode of attack, especially if the warhead has a thermobaric filler, presents much better odds of success, as a large scale fire can be produced which can destroy stored materiel, including aircraft, POL,  and stored munitions. After such an attack the underground hangar will likely still be repairable, but may require significant rebuilding as fires will destroy or severely damage internal cladding, wiring looms and plumbing, while leaving hazardous residues and UXO in the hangar cavities. In a high intensity short duration conflict this mode of attack would render the target unusable for the duration of the conflict.

The drawback of “flying the bomb in through the front door” attacks is that in many locations, the simple expedient of placing a berm, reinforced concrete entrance blocker, or burster slab in front of the hangar entrance would preclude such attacks. This method is infeasible where the entry to the hangar is in a deep canyon cut into a hillside, but such locations would in turn permit the installation of sacrificial prestressed concrete burster slabs or deflection grids over the entrance, to force the inbound weapon to initiate early, outside the main blast doors5.

At least one underground hangar equipped base in the DPRK, designed to the PLA pattern, incorporates a blocking structure in front of the hangar entrance6.

The notion that the PLA, being as well versed as it is in airfield construction and passive defence, would not deploy such simple and cheap protective measures at such important sites is not realistic. The technology and design technique for burster slabs and deflection grids is relatively mature, and well within the reach of China's indigenous civil and construction engineering capabilities. China has an abundance of earthmoving equipment and experienced construction workers.



The “conventional” approach to attacking hardened structures is from above or the sides. This example shows attack into the rock above the entrances. The intent would be to collapse the tunnels at either entrance from above.

The only robust “quick kill” tactic against an underground hangar with a high probability of causing the hangar cavity to cave in, thus rendering it permanently unusable, is the use of the GBU-57A/B Massive Ordnance Penetrator, or a similar “earthquake bomb” class munition. In well defended airspace, such as China's Eastern IADS sectors, this would require delivery by very scarce B-2A bombers. To effect a robust kill against a typical PLA underground hangar would require multiple well placed GBU-57/B hits, reflecting the extensive Royal Air Force operational experience of the 1940s using the Tallboy and Grand Slam “earthquake bombs” to destroy underground structures.

The British experience with the use of the Tallboy and Grand Slam was that despite the exceptional penetration performance of these weapons, many targets with unusually strong rock or concrete roofs were difficult to defeat, as the weapon could not penetrate the dense materials deeply enough to produce the intended effect. This would be an issue for attack on underground hangars where the hill or mountain was of an igneous rock composition, such as granites, basalts, diorites or serpentines. Such rock is often both hard and tough, which limits penetration depth strongly in comparison with sedimentary rock types.

The strategy used by the British with considerable success was to put the bomb next to the target, into softer materials, such that the shock effect hit the target from the sides or below, where it was less able to absorb the load and would collapse as a result.

Study of PLA underground hangar construction shows tunnels with a weighted catenary arch cross section, intended as in the design of bridges or other structures using catenaries, to transfer compressive loads produced by the weight of the rock above, outward into the lower sides of the tunnel. The compressive shock loads even from large conventional bombs, or airburst nuclear weapon overpressure, hitting above the tunnels would be transferred by the catenary section into horizontal compressive loads in the rock.

The weakness of this design is that a latent tensile load exists in the tunnel floors, resulting from the compressive force on the lower tunnel walls.

Attack with a GBU-57A/B aimed at the apron infront of each tunnel entrance would generate a shock pulse with a large component pushing the tunnel floor upward, and thus increasing the tensile load on the tunnel floors. While reinforced concrete has some tolerance for tensile loads, rock typically does not, moreso if the load is cyclic, or repeated. Such an attack therefore has the potential to collapse the tunnel from below, by causing the floor to burst into the cavity. Even modest damage levels would present difficulties by impairing aircraft movements over a fractured floor, with significant potential for spalling damage from delaminated concrete fragments.



The “Wallis” approach to attacking hardened structures is from below and the side. This example shows attack into the apron in front of the hangar entrances. The intent would be to collapse the tunnels at either entrance from below.





Counter-PGM weapons such as this LD-2000 30 mm Gatling SPAAG (above) could significantly complicate defeat of PLA airbases equipped with underground hangars, by attritting penetrating PGMs prior to impact. The LD-2000 is a derivative of the Type 730 CIWS (below), itself a Chinese copy of the Thales Nederland Goalkeeper, with the  Type 730B gun a copy of the General Electric GAU-8 Avenger 30 mm x 173 mm seven-barrel  gun used on the A-10 Warthog. The LD-2000 was recently integrated with a CBR to perform the C-RAM role (Chinese Internet).





The Russian Kupol 9K332 Tor M2E / SA-15D Gauntlet was specifically developed to engage and defeat saturation PGM attacks against critical infrastructure, as a competitor to the KBP 96K6 Pantsir S1E / SA-22  SPAAGM. The PLA operates the earlier and less capable 9K331M1 Tor M1 SAM. Depicted example is deployed (Strizhi.info).



The high destructive effect and procurement cost of large munitions such as the GBU-57A/B MOP would easily justify the use of area defence SAMs such as the HQ-12 or HQ-9 to intercept such PGMs after release. Left: HQ-12/KS-1A TELs and H-200 engagement radar; right: HQ-9 TEL and HT-233 engagement radar (via Chinese Internet).

Defensive Measures Available for Survivability Enhancement of Underground Hangars
Measure
Category
Effectiveness
Cost
SDB
JDAM
MOP
Entrance Burster Slabs
Passive
High Low Low
Entrance Blocking Structures
Passive High Low Low
Entrance Deflection Grids
Passive High Low Low
Redundant Entrances and Access Tunnels
Passive High High
Site dependent
Procure/Deploy 9K332 Tor M2E / SA-15D Gauntlet SAM
Active
High High
High
Procure/Deploy 96K6 Pantsir S1E / SA-22  SPAAGM
Active High High
High
Evolve/Deploy LD-2000 SPAAGM C-PGM Variant
Active High Low Modest
Evolve/Deploy HQ-7B/FM-90 Crotale C-PGM Variant
Active High Low Modest
Evolve/Deploy HQ-6D/LY-60 Aspide C-PGM Variant Active High Low Modest
Redeploy HQ-12/KS-1A Batteries
Active Low High Modest
Procure/Deploy HQ-9 Batteries Active Low High Modest - High
Procure/Deploy S-300PMU2 / SA-20 Batteries Active Low High High
Table 2.

Active defence of airfields using AAA, SPAAG and SAM systems is a well established aspect of PLA doctrine, and HQ-7 and HQ-6D/HQ-64 batteries have been observed in close proximity to airfields, the intent being to engage low flying aircraft and cruise missiles. Once the PLA follows the Russian lead in deploying point defence weapons, such as SPAAGs, SPAAGMs and SAMs, in the Counter-PGM role, even a single battery of such weapons  at each airfield would significantly complicate the defeat of underground hangar equipped airbases.

Importantly, a large PGM such as the GBU-57A/B MOP is valuable and destructive enough in its own right to justify its engagement with an area defence SAM system as early as possible after release. An area defence SAM system such as the HQ-12, HQ-9, S-300PMU/PMU1/PMU2 is kinematically compatible with such a target, and the cost of two or more rounds expended is easily justified given the damage effects such a weapon can produce7.

Passive defence measures for underground hangars, other than the use of additional burster slabs, blocking structures and deflection grids at entrances, include the simple expedient of adding additional hangar entrances and access tunnels by further excavation, at extant sites. Most PLA underground hangars employ two entrances only. Doubling the number of entrances and access tunnels doubles the necessary effort to disable these sites, with proportionate increases for further entrances and access tunnels. This application of redundancy, in effect using Lusser's product law, has the additional benefit of further increasing hangar internal capacity, and yielding bulk spoil which can be employed to further enhance passive defence measures elsewhere at the site.

Table 2 summarises available active and passive defensive measures, and compares their effectiveness against smaller penetrating munitions, such as the GBU-39/B and JDAM derivatives, and the much larger GBU-57A/B MOP.

In pragmatic terms, the PLA's network of superhardened underground airbases would present a genuine challenge to defeat without the possession of a well sized fleet of stealthy heavy bombers, and a very robust warstock of hundreds of GBU-57A/B rounds reserved for this purpose. As such, these superhardened underground airbases are an extremely valuable strategic asset, without peer globally, as they make a rapid “knockout blow” massed attack on PLA airfields operationally infeasible even for the United States at this time8.



How much effort is required to disable a typical PLA airbase equipped with an underground hangar? This chart presents a hypothetical targeting model for such a base, assuming the use of the GBU-39/B SDB and GBU-57A/B MOP. No less than 51 SDBs are required cover key airbase facilities, and two MOPs to defeat the underground hangar system. While the MOP requires the use of the B-2A, the SDB could be delivered by both the B-2A and the F-22A. No less than seven F-22A sorties would be required to deliver the required number of SDBs. Forty such bases would require forty-fold the number of weapons delivered (S. O'Connor).


This chart shows the pronounced asymmetry between the PLA's robust basing infrastructure, in comparison with that of the United States, and its principal WestPac allies, Japan and Australia. The chart excludes civil airfields, dual use airfields and PLA military airfields in the two Western MRs. The PLA has available around 150 military airfields, divided not quite evenly between superhardened bases with underground hangars, bases equipped with revetments or HAS, and unhardened bases. In a “PGM-centric” warfighting environment, bases with revetments qualify as unhardened. With around seven times the number of military airbases available, the PLA has a major advantage over the US and its allies, in terms of its ability to rapidly relocate combat units, or redeploy if a base is severely damaged. The number of superhardened bases with underground hangars alone is around twice the total number of operational bases used by the United States, and its principal WestPac allies, Japan and Australia. Whether we consider scenarios involving pre-emptive attacks, or sustained air wars of attrition, China has an enormous advantage over the United States, and its allies, as the asymmetry in basing infrastructure produces a strong asymmetry in military effort required to degrade airbase operational capability, attrit aircraft on the ground, or render basing unusable. An excellent analysis of this problem was produced by Stillion9.


Conclusions


The PLA's network of around forty underground airbases provides a unique and indeed exceptionally robust capability to withstand a large scale counter-air campaign, as significant effort with penetrating munitions of large mass would be required to close such bases down for the duration of the campaign, or permanently render them unusable.

As these bases deny surveillance by orbital, airborne or ground based ISR assets, they provide an inherent capability to perform covert preparations for combat operations, be it in times of conflict, or in the period immediately preceding a conflict.

The hangaring capacity of these underground bases is of the order of at least 1,500 combat aircraft, possibly greater,  if more than basic internal tunnel arrangements have been employed.  This capacity represents more than the total number of modern combat aircraft currently operated by the PLA, and thus provides the PLA with the capability to protect its best assets during any major conflict where opposing aircraft would seek to attack PLA air bases.

At this time there is no evidence that the PLA has been favouring the use of its underground basing in the operational deployment of units operating newer combat aircraft, as these are operated both from bases with and without underground hangars. However, peacetime deployment patterns do not necessarily reflect intended deployment patterns in times of conflict, or in the period immediately preceding a conflict. The PLA has not shared its thinking on the use of these bases in war, and is very unlikely to do so in the forseeable future.

In strategic terms, the PLA's underground airbase infrastructure provides a capability to deny  at this time any feasible opponent, even the United States, the opportunity to inflict massive early attrition upon the PLA's fleet of combat aircraft while these are on the ground. This would force any opponent, including the United States, into a protracted aerial war of attrition, in which repeat attacks on hardened airbases would be required, over a period of many weeks or months, before decisive attrition could be inflicted upon the PLA combat aircraft fleet.

The inherent survivability of the PLA's superlative underground airbase infrastructure has not been a major consideration in ongoing debate in the United States on the utility, and indeed intended design, of its replacement heavy bomber aircraft. If the defeat of the PLA's underground airbase infrastructure is part of the intended role of this future aircraft, then this aircraft will need to combine the survivability needed to repeatedly penetrate what is becoming the best Integrated Air Defence System in existence, with the ability to deliver heavy “earthquake bombs”. Any lesser capability would result in unsustainable combat attrition.

While China's underground airbase infrastructure may well be an artefact of the early Cold War period, it will clearly have an enduring long term impact as one of China's invaluable national strategic assets.


Endnotes/References/Bibliography


  1. Saumur Tunnel, 9th June 1944, Royal Air Force website: URI: http://www.raf.mod.uk/bombercommand/saumur.html; Royal Air Force Bomber Command 60th Anniversary
    Campaign Diary, June 1944, URI: http://www.raf.mod.uk/bombercommand/jun44.html.

  2. Glasstone S, Dolan P.J., The Effects of Nuclear Weapons, Third Edition, US DOD and ERADA, 1977, URI: http://www.atomicarchive.com/Docs/Effects/index.shtml.
  3. Kopp C., Hardening RAAF Air Base Infrastructure, APA Analyses, Vol. V APA-2008-02, URI: APA-2008-02.html; Kopp C., The GBU-28 Bunker Buster, Technical Report APA-TR-2005-0501, URI: GBU-28.html; Kopp C., GBU-39/B Small Diameter Bomb I, Technical Report APA-TR-2007-0106, URI: APA-SDB.html.
  4. Some measure of the effort required to excavate a single underground hangar can be gained by estimating the tonnage of rock to be removed. If we assume a semicircular cross-section with a diameter of 13 metres, and a length of 500 metres, the total volume is ~33,200 m3. At 2.5 to 3 tonnes per cubic metre, this is up to 100,000 tonnes of rock per base, or more if a complex tunnel arrangement is employed.
  5. Burster slabs are employed to force the penetrating weapon to initiate early, and to deflect the blast overpressure, while deflection grids are employed to impart a normal acceleration to a penetrating munition to cause its casing to burst or bend, impairing its ability to penetrate. Both are relatively simple to construct. A good discussion of the design principles of these can be found in: Slawson T.R. et al, Design of an Underground Facility Subjected to CWE and Accidental Threats, Technical Report, US Army Corps of Engineers, Omaha District, Omaha, NE, 61802-4901, August, 1994; and Underwood J.M., EFFECTIVENESS OF YAW-INDUCING DEFLECTION GRIDS FOR DEFEATING ADVANCED PENETRATING WEAPONS, Technical Report, ESL-TR-92-61, ENGINEERING RESEARCH DIVISION, Air Force Civil Engineering Support Agency, Civil Engineering Laboratory, Tyndall Air Force Base, Florida 32403, April, 1995.
  6. O'Connor S., Underground Airfields: The DPRK, GEIMINT Blog, URI: http://geimint.blogspot.com/2010/07/underground-airfields-dprk.html.
  7. The likelihood of defensive missile attacks against the GBU-57A/B indicates that self protective measures should be added. This is not a new idea, as the Soviet AV-MF included self-protection jammers on the P-500 Bazalt / SS-N-12 Sandbox cruise missile. Obvious choices are an internal RF jammer, or a towed decoy.
  8. The strategic reality is that had the United States built and deployed the initially planned fleet of 132 B-2A bombers, or even half that number, this force structure gap problem would not exist now.
  9. Stillion J., Fighting Under Missile Attack, Air Force Magazine, Vol. 92, No. 8, August, 2009, URI: http://www.airforce-magazine.com/MagazineArchive/Pages/2009/August%202009/0809fighting.aspx
  10. Kopp C., People's Liberation Army Air Force and Naval Air Arm Air Base Infrastructure, Technical Report APA-TR-2007-0103, January, 2007, URI: APA-PLA-AFBs.html.
  11. O'Connor S., Chinese Military Airfields, GEIMINT Blog, URI: http://geimint.blogspot.com/2008/12/chinese-military-airfields.html.
  12. Bowie C.J., The Lessons of Salty Demo, Air Force Magazine, Vol.92, No.3, March 2009, URI: http://www.airforce-magazine.com/MagazineArchive/Pages/2009/March%202009/0309salty.aspx
  13. Chinese Air Arms, Scramble.nl, URI: http://www.scramble.nl/cn.htm
  14. Chris Lofting, Albanian Airbase Imagery (Photoessay), Airliners.net, URI: http://www.airliners.net/search/photo.search?id=1052618,1166446,1183226,1183229,1142666,1134330,1052623,1079196,1119821,1206364
  15. Holger Mueller, Albania 2006 (Photoessay), MiG-21.de, URI: http://www.mig-21.de/english/newsarchive/albania2006.htm
  16. Stillion J., Orletsky D.T., Airbase Vulnerability to Conventional Cruise-Missile and Ballistic-Missile Attacks; Technology, Scenarios, and U.S. Air Force Responses, Monograph MR-1028, Project Air Force, RAND Corporation, URI: http://www.rand.org/pubs/monograph_reports/MR1028.html.
  17. Kopp C., EXPANDING THE ENVELOPE - Stealth and Other Strike Roles, Air & Space Power Chronicles, Maxwell AFB, July 2000, URI: http://www.airpower.maxwell.af.mil/airchronicles/cc/kopp.html.
  18. Bowie C.J., The Lessons of Salty Demo, Air Force Magazine, Vol.92, No.3, March 2009, URI: http://www.airforce-magazine.com/MagazineArchive/Pages/2009/March%202009/0309salty.aspx
  19. Centner C.M., IGNORANCE IS RISK; THE BIG LESSON FROM DESERT STORM AIR BASE ATTACKS, Airpower Journal, Winter 1992, URI: http://www.airpower.maxwell.af.mil/airchronicles/apj/apj92/win92/centner.htm.
  20. Blake T.C., Improving the Ground Survivability of In-Theater TACAIR, Air University Review, September-October 1975, URI: http://www.airpower.au.af.mil/airchronicles/aureview/1975/sep-oct/blake.html.
  21. Satellite imagery provided courtesy of Google Earth.
  22. Imagery Sources: US DoD; PLA-AF, PLAN-AF; MilitaryPhotos.net; other Internet sources.
  23. Updated 23rd February, 2011, add Albanian imagery by Holger Müller.
  24. Updated 28th February, 2011, add Albanian layout diagrams by Roland Büchler; Annex C.3 with blast door designs.




The only current and planned US assets capable of surviving China's growing IADS are the B-2A Spirit and and F-22A Raptor. Intended numbers in the force structure are only a small fraction of that necessary to defeat the growing capability of the PLA-AF (US Air Force image).


Acknowledgements


The authors are greatly indebted to all parties in Australia and overseas who reviewed the draft of this paper, for their cogent comments and valuable thoughts.



A formation of Harbin H-5 Beagle bombers. At least fourteen underground hangar systems were constructed  during the Cold War to protect these aircraft (via Chinese Internet).


Annex A - PLA Underground Air Base Survey


The satellite images in this survey were captured using Google Earth in early 2011, and mostly reflect LEO satellite imagery collected over the previous four years. Image quality varies and results in some uncertainty in some of the airbase assessments. The survey datasets employed were produced by the authors previously7, 8.

Criteria for determining the presence of an underground hangar were thus:
  1. The hangar must be under a hill or other terrain with credible elevation to provide viable protective depth of rock;
  2. Taxiways and where applicable an auxiliary runway of appropriate width and surface quality must exist connecting the runway system to the hangar entrances;
  3. Entrance geometry and size must be consistent with well known PLA underground hangars previously identified, and must match taxiway widths and clearances;
  4. The airbase is a known PLA airfield with a prior history, and reflects PLA design practice and layout;
  5. Where possible, supporting evidence such as declassified KH-4 imagery is to be used to validate observations;
A number of sites were found which initially presented as possible underground hangar sites, but were reclassified as weapons bunkers if they did not meet the preceding validation criteria, and are not listed in this Annex.

In most instances the underground hangar is situated within 1 to 2 kilometres distance from the taxiway exit from the runway system, although a few notable examples involve greater distances.

A number of PLA airfields have been constructed within suitable distance of a hill, mountain, or elevated terrain, for an underground hangar to be constructed, but in the absence of taxiways or roads connecting to the runway system, were assessed as bases without an underground hangar. Such bases could be equipped with an underground hangar at a future date.

Of the total number of airfields with identified underground hangars, one is derelict and overbuilt,  two appear to be mothballed or unused, one requires repairs to the end of runway,  and three require taxiway or auxiliary runway repairs.

The authors make no warranty that this survey is complete, and that other underground hangars do not exist at other locations in China.


  1. PLA-AF Fuxin AB / Shenyang MR
  2. PLA-AF Jichang AB / Shenyang MR
  3. PLA-AF Jinzhou Xiaolingzi AB / Shenyang MR
  4. PLA-AF Lihue AB / Shenyang MR
  5. PLA-AF Nangangzi AB / Shenyang MR
  6. PLA-AF Beijing Shahezhen AB [Datangshan] / Beijing MR
  7. PLA-AF Chen-Chuan AB / Beijing MR
  8. PLA-AF Chifeng AB / Beijing MR
  9. PLA-AF Fengning AB / Beijing MR
  10. PLA-AF Hohhot AB / Beijing MR
  11. PLA-AF Jizhuang AB / Beijing MR
  12. PLA-AF Pingquan AB / Beijing MR
  13. PLA-AF Wenshui AB / Beijing MR
  14. PLA-AF Yongning AB / Beijing MR
  15. PLA-AF Zhangjiakou AB / Beijing MR
  16. PLA-AF Zunhua AB / Beijing MR
  17. PLA-AF Urumqi South AB / Lanzhou MR
  18. PLA-AF Yinchuan / Xincheng AB / Lanzhou MR
  19. PLA-AF Anqing AB (An Ching) / Nanjing MR
  20. PLA-AF Changzing AB / Nanjing MR
  21. PLA-NAF Daishan Island AB / Nanjing MR
  22. PLA-NAF Feidong AB / Nanjing MR
  23. PLA-AF Suzhou West AB / Nanjing MR
  24. PLA-AF Taihe AB / Nanjing MR
  25. PLA-NAF Yiwu AB / Nanjing MR
  26. PLA-NAF Ledong / Foluo Northeast AB / Guangzhou MR
  27. PLA-NAF Guiping Mengshu AB / Guangzhou MR
  28. PLA-AF Leng Shui Chi AB / Guangzhou MR
  29. PLA-AF Shaodong AB / Guangzhou MR
  30. PLA-AF Shaoguan AB / Guangzhou MR
  31. PLA-AF Wudangshan AB / Guangzhou MR
  32. PLA-AF Yaotian AB / Guangzhou MR
  33. PLA-AF Guodu AB / Jinan MR
  34. PLA-AF Jining AB / Jinan MR
  35. PLA-AF Jiyuan AB / Jinan MR
  36. PLA-AF Luyang / Ranghe Zhen AB / Jinan MR
  37. PLA-AF Neixiang  AB / Jinan MR
  38. PLA-AF Yantai Southwest  AB / Jinan MR
  39. PLA-AF Yidu/Chijian  AB / Jinan MR
  40. PLA-AF Guiyang AB / Chengdu MR
  41. PLA-AF Wenshan/Pinquan  AB / Chengdu MR

CHINAUGFSHENYANG

Shenyang MR Underground Airbases, Geographical Placement [Click to enlarge].


PLA-AF Fuxin AB / Shenyang MR


Coordinates: 42° 4' 44N 121° 39' 43E
Base Primary R/W: 08/280
Base Primary R/W Length: 7,200 ft
Base Status / Tenant: Unknown

PLA-Fuxin-AB-UGH-2011-3
PLA-Fuxin-AB-UGH-2011-1
PLA-Fuxin-AB-UGH-2011-2






Fuxin AB employs a conventional layout, but is devoid of an auxiliary runway due to the very close proximity of the runway to the hangar entrances. It is a fighter base with 15 metre hangar entrances.


PLA-AF Jichang AB / Shenyang MR


Base Location: 43° 12'N 125° 53'E
Base Primary R/W: 08/26
Base Primary R/W Length: 7,100 ft
Base Status / Tenant: Unknown

PLA-Jichang-AB-UGH-2011-1
PLA-Jichang-AB-UGH-2011-3
PLA-Jichang-AB-UGH-2011-2


PLA-Jichang-AB-UGH-2011-4



Jichang AB is unusual in that it employs two separate underground hangars in two hills adjacent to the main apron and taxiway. This former H-5 Beagle base has four 22 metre entrances.


PLA-AF Jinzhou Xiaolingzi AB / Shenyang MR


Base Location: 41° 6'3.98"N 121° 3'47.38"E
Base Primary R/W: 01/19
Base Primary R/W Length: 8,500 ft
Base Auxiliary R/W: 12/30
Base Auxiliary R/W Length: 5,800 ft
Base Status / Tenant: 3rd FA trainers

PLA-Jinzhou-Xiaolingzi-AB-UGH-2011-3
PLA-Jinzhou-Xiaolingzi-AB-UGH-2011-1
PLA-Jinzhou-Xiaolingzi-AB-UGH-2011-2






This base was constructed to house interceptors, and is equipped with an auxiliary runway, and two 15 metre hangar entrances.


PLA-AF Lihue AB / Shenyang MR


Base Location:  42°15'16.42"N / 125°42'19.39"E
Base Primary R/W: 04/22
Base Primary R/W Length: 7,200 ft
Base Auxiliary R/W: 16/24
Base Auxiliary R/W Length: 6,500 ft
Base Status / Tenant:

PLA-Lihue-AB-UGH-2011-1
PLA-Lihue-AB-UGH-2011-2
PLA-Lihue-AB-UGH-2011-3






Lihue is an active fighter base, constructed with a 40 m wide auxiliary runway and an underground hangar located in a canyon between two mountains South of the base. Two entrances provide access to an estimated 800 m hangar. Imagery resolution precludes at this time accurate entrance width assessment, which could be in excess of 20 metres. In addition the base has fifteen conventional revetments at the southern apron.


PLA-AF Nangangzi AB / Shenyang MR


Base Location:  43°48'56.35"N / 127°30'25.28"E
Base Primary R/W: 01/19
Base Primary R/W Length: ~6,400 ft usable
Base Status / Tenant: Unknown

PLA-Nangangzi-AB-UGH-2011-1
PLA-Nangangzi-AB-UGH-2011-2
PLA-Nangangzi-AB-UGH-2011-3






Nangangzi AB is a former H-5 bomber base, with two 20 metre entrances to an underground hangar in the mountain immediately to the West of the runway system. There is no evidence of recent operational activity, and the northern end of the main runway is in a state of disrepair, with only ~6,400 ft of the 7,100 ft evidently in usable condition. The internal length of the hangar is ~800 metres.



CHINAUGFBEIJING

Beijing MR Underground Airbases, Geographical Placement [Click to enlarge].


PLA-AF Beijing Shahezhen AB [Datangshan] / Beijing MR


Base Location:
Base Primary R/W: XX/YY
Base Primary R/W Length: ZZZZ ft
Base Status / Tenant: XXth FD / YYth AR

PLA-Shahezhen-AB-UGH-2011-1


PLA-Datangshan-UGH-2011-1






Datangshan, situated in the outer Beijing suburbs, has two 33 metre entrances for the H-6 Badger. The site has been redeveloped as the China Aviation Museum, housing a large collection of aircraft dating to the 1940s.


PLA-AF Chen-Chuan AB / Beijing MR


Base Location:  37°52'23.26"N / 110° 4'17.29"E
Base Primary R/W: 14/32
Base Primary R/W Length: 8,500 ft
Base Status / Tenant: Unknown

PLA-Chen-Chuan-AB-UGH-2011-1
PLA-Chen-Chuan-AB-UGH-2011-2
PLA-Chen-Chuan-AB-UGH-2011-3






This base was initially constructed to operate the H-5, and is equipped with an underground hangar with two colocated 22 metre entrances, and an internal length of at least 600 metres. The base does not display evidence of recent operational activity.


PLA-AF Chifeng AB / Beijing MR


Coordinates: 42° 9' 32N 118° 50' 31E
Base Primary R/W: 02/20
Base Primary R/W Length: 8,100 ft
Base Auxiliary R/W: 01/19
Base Auxiliary R/W Length: 7,000 (5,900) ft
Base Status / Tenant: 1st FD J-7E / Unknown AR

PLA-Chifeng-AB-UGH-2011-3
PLA-Chifeng-AB-UGH-2011-2
PLA-Chifeng-AB-UGH-2011-1






The Chifeng fighter base employs an unusual placement for the auxiliary runway, which appears to be under repair in available imagery, and partly overgrown with foliage. Twenty eight lightweight shelters have been constructed on the primary apron. The  two hangar entrances are 13 metres wide.


PLA-AF Fengning AB / Beijing MR


Base Location: 41°15'39.31"N / 116°37'8.91"E
Base Primary R/W: 17/35
Base Primary R/W Length: 7,500 ft
Base Status / Tenant: Unknown

PLA-Fengning-AB-UGH-2011-3
PLA-Fengning-AB-UGH-2011-2
PLA-Fengning-AB-UGH-2011-1






Fengning is a fighter base, lacking an auxiliary runway, with a dual entrance underground hangar with 15 metre entrances.


PLA-AF Hohhot AB / Beijing MR


Base Location: 40°44'19.38"N / 111°13'46.22"E
Base Primary R/W: 08/26
Base Primary R/W Length: 7,800 ft
Base Status / Tenant: J-7II, J-7E FD / unknown AR

PLA-Hohhot-AB-UGH-2011-3
PLA-Hohhot-AB-UGH-2011-1
PLA-Hohhot-AB-UGH-2011-2






Hohhot is a fighter base with two 15 metre entrances colocated on the southern side of the mountain, to the west of the runway system. At least two squadrons of Fishbeds have been observed at this site.


PLA-AF Jizhuang AB / Beijing MR


Base Location: 38°35'50.20"N / 112°58'8.80"E
Base Primary R/W: 07/25
Base Primary R/W Length: 8,200 ft
Base Status / Tenant: Unknown FD

PLA-Jizhuang-AB-UGH-2011-1
PLA-Jizhuang-AB-UGH-2011-2
PLA-Jizhuang-AB-UGH-2011-3






Jizhuang is a fighter base with two 15 metre entrances on southern side of the mountain, to the northeast of the runway system. The estimated minimal length of the hangar is 700 m.


PLA-AF Pingquan AB / Beijing MR


Base Location:  40°53'52.41"N / 118°40'53.63"E
Base Primary R/W: 06/24
Base Primary R/W Length: 7,800 ft
Base Status / Tenant: Unknown

PLA-Pingquan-AB-UGH-2011-3
PLA-Pingquan-AB-UGH-2011-1
PLA-Pingquan-AB-UGH-2011-2






This former H-5 Beagle base has three 22 metre entrances on the southern side of the mountain.


PLA-AF Wenshui AB / Beijing MR


Base Location:  37°24'30.17"N / 111°57'55.62"E
Base Primary R/W: 06/24
Base Primary R/W Length: 10,400 ft
Base Status / Tenant: 8th BD H-6

PLA-Wenshui-AB-UGH-2011-1
PLA-Wenshui-AB-UGH-2011-2
PLA-Wenshui-AB-UGH-2011-3






Wenshui was until recently an operational PLA-AF H-6 Badger base, with a large 10,400 ft primary runway. The site is equipped with a 40 metre wide dual entrance underground hangar located under a mountain 3 kilometres NW of the Western end of the runway. Estimated length of the hangar is ~600 metres.


PLA-AF Yongning AB / Beijing MR


Base Location: 40°30'14.69"N  / 116° 6'22.71"E
Base Primary R/W: 05/28
Base Primary R/W Length: 7,500 ft
Base Status / Tenant: J-7 FD / Unknown AR

PLA-Yongning-AB-UGH-2011-3
PLA-Yongning-AB-UGH-2011-1
PLA-Yongning-AB-UGH-2011-2






This former H-5 Beagle base has a pair of 22 metre  underground hangar entrances, with the western taxiway partly overgrown with foliage.


PLA-AF Zhangjiakou AB / Beijing MR


Base Location: 40°44'15.98"N / 114°55'51.02"E
Base Primary R/W: 11/29
Base Primary R/W Length: 8,100 ft
Base Status / Tenant: 7th FD / 9th AR J-11

PLA-Zhangjiakou-AB-UGH-2011-3
PLA-Zhangjiakou-AB-UGH-2011-1
PLA-Zhangjiakou-AB-UGH-2011-2






Zhangjiakou is a fighter base equipped with two underground hangars, each of which has a pair of 15 metre entrances. The base lacks an auxiliary runway. While the base hosts a J-11 Air Regiment, these are incompatible with the hangar system, which was built for the J-6/J-7.


PLA-AF Zunhua AB / Beijing MR


Base Location: 40° 6'23.74"N / 117°53'10.20"E
Base Primary R/W: 07/25
Base Primary R/W Length: 7,900 ft
Base Auxiliary R/W: 02/14
Base Auxiliary R/W Length: 5,200 ft
Base Status / Tenant: 24th FD J-8 / Unknown AR

PLA-Zunhua-AB-UGH-2011-3
PLA-Zunhua-AB-UGH-2011-1
PLA-Zunhua-AB-UGH-2011-2






Zunhua is an auxiliary runway equipped fighter base, with a pair of colocated 15 metre hangar entrances, at the north end of the unusually wide auxiliary runway.



CHINAUGFLANZHOU

Lanzhou MR Underground Airbases, Geographical Placement [Click to enlarge].


PLA-AF Urumqi South AB / Lanzhou MR


Base Location: 43°27'57.91"N / 87°31'56.45"E
Base Primary R/W: 09/27
Base Primary R/W Length: 9,100 ft
Base Status / Tenant: 37th FD / 110th AR (J-8F), 111th AR (J-7II)

PLA-Urumqi-South-AB-UGH-2011-3
PLA-Urumqi-South-AB-UGH-2011-2
PLA-Urumqi-South-AB-UGH-2011-1






Urumqi is a remote fighter base, without an auxiliary runway. The underground hangar with a pair of colocated 15 metre entrances is 3.5 kilometres south of the base.


PLA-AF Yinchuan / Xincheng AB / Lanzhou MR


Base Location:
Base Primary R/W: 01/19
Base Primary R/W Length: 9,100 ft
Base Auxiliary R/W: 12/30
Base Auxiliary R/W Length: 6,500 ft
Base Status / Tenant: 6th FD / 140th AR (Su-27SK/UBK)

PLA-Yinchuan-Xincheng-AB-UGH-2011-3
PLA-Yinchuan-Xincheng-AB-UGH-2011-1
PLA-Yinchuan-Xincheng-AB-UGH-2011-2






Yinchuan superficially appears to be a typical fighter base with an auxiliary runway. The underground hangar system is however equipped with four entrances, two of which are 15 metres wide, and two 22 metres wide. It is likely the base was initially shared between J-6 and H-5 units. Twenty four lightweight shelters are constructed on the central apron.



CHINAUGFNANJING

Nanjing MR Underground Airbases, Geographical Placement [Click to enlarge].

PLA-AF Anqing AB (An Ching) / Nanjing MR


Base Location:
Base Primary R/W: 06/24
Base Primary R/W Length: 9,500 ft
Base Auxiliary R/W: 14/32
Base Auxiliary R/W Length: 6,500 ft
Base Status / Tenant: 10th BD H-6, Y-8(EW)

PLA-Anqing-AB-UGH-2011-3
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An Ching was initially constructed as a fighter base, equipped with an auxiliary runway and an underground hangar, built with paired 15 metre entrances. The base was later redeveloped and now hosts H-6 Badgers of the 10th Bomber Division. While some sources claim an underground hangar for the H-6 aircraft, there is no evidence of such.



KH-4 Corona wet film imagery of An Ching AB in Nanjing MR, collected 1962-1963, showing underground hangar access (US DoD via FAS).


PLA-AF Changzing AB / Nanjing MR


Base Location:  30°58'14.07"N / 119°43'46.08"E
Base Primary R/W: 07/11
Base Primary R/W Length: 8,300 ft
Base Auxiliary R/W: 10/28
Base Auxiliary R/W Length: 4,500 ft
Base Status / Tenant: 3rd FD J-7II, J-10 / Unknown AR

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This former H-5 Beagle base has a pair of 22 metre entrances, and an auxiliary runway.


PLA-NAF Daishan Island AB / Nanjing MR


Base Location:  30°17'12.71"N / 122° 8'34.30"E
Base Primary R/W: 02/20
Base Primary R/W Length: 7,500 ft
Base Auxiliary R/W: 10/28
Base Auxiliary R/W Length: 6,500 ft
Base Status / Tenant: Currently unused

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The Daishan Island interceptor base was previously operated by the PLAN, providing local air defence for the Shanghai Bay area. It has a dual entrance underground hangar with narrow 13 metre entrances, one of these is now blocked. The auxiliary and primary runways are in a state of disrepair, and the taxiways are being used as sealed bitumen roads.



A 1962 KH-4 Corona image of the Daishan Island interceptor base. To the top of the image is the hill to the West of the runway system, and associated taxiway, which still shows today evidence of excavations into the base of the hill, along the Western base taxiway (US DoD via FAS).


PLA-NAF Feidong AB / Nanjing MR


Base Location: 31°54'39.07"N / 117°39'58.71"E
Base Primary R/W:
04/22
Base Primary R/W Length: 8,500 ft
Base Auxiliary R/W: 14/32
Base Auxiliary R/W Length: 5,600 ft
Base Status / Tenant: 4th FD / 12th AR (Su-30MK2)

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This former H-5 Beagle base has a pair of 22 metre entrances, and an auxiliary runway. Twenty four lightweight shelters have been constructed on the central apron.


PLA-AF Suzhou West AB / Nanjing MR


Base Location: 31°15'46.75"N / 120°24'8.00"E
Base Primary R/W: 18/36
Base Primary R/W Length: 8,200 ft
Base Status / Tenant: Unknown FD / 2 x J-6, 1 x J-7 AR

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Suzhou West is a former H-5 Beagle base with a pair of 22 metre entrances to an underground hangar,  north-east of the runway system.


PLA-AF Taihe AB / Nanjing MR


Base Location: 26°51'30.16"N / 114°44'15.07"E
Base Primary R/W: 08/26
Base Primary R/W Length: 8,700 ft
Base Auxiliary R/W: 04/22
Base Auxiliary R/W Length: 5,900 ft
Base Status / Tenant: 2nd IR JZ-6

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Taihe is a former H-5 Beagle base with a pair of 22 metre entrances to an underground hangar, and an auxiliary runway.


PLA-NAF Yiwu AB / Nanjing MR


Base Location: 29°20'43.73"N / 120° 2'4.10"E
Base Primary R/W: 02/20
Base Primary R/W Length: 8,500 ft
Base Auxiliary R/W: 16/34
Base Auxiliary R/W Length: 6,000 ft
Base Status / Tenant: 6th GAD PLAN 17th AR JH-7; formerly 26th FD PLA-AF

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Yiwu is a former H-5 Beagle base with a pair of 22 metre entrances to an underground hangar, and an auxiliary runway.



KH-4 Corona wet film imagery of Yiwu AB in Nanjing MR, collected 1962-1963, showing underground hangar access (US DoD via FAS).



CHINAUGFGUANGZHOU

Guangzhou MR Underground Airbases, Geographical Placement [Click to enlarge].


PLA-NAF Ledong / Foluo Northeast AB / Guangzhou MR


Base Location: 18°41'34.56"N / 109° 9'40.84"E
Base Primary R/W: 04/22
Base Primary R/W Length: 9,300 ft
Base Auxiliary R/W: 14/32
Base Auxiliary R/W Length: 7,300 ft
Base Status / Tenant: 9th FD / 27th AR (JH-7A)

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The Foluo NorthEast airbase on Hainan Island is of an unusual configuration. While it has an auxiliary runway and underground hangar in the fashion of a typical fighter base, the main runway, auxiliary runway and underground hangar entrances are 40+ metres wide, sized for the H-6 Badger. Twenty four lightweight shelters have been built on the main apron, for 27th Air Regiment JH-7A Flounder aircraft.

Kristensen of FAS noted that the Foluo NE underground hangar was under active construction circa 2005, but satellite imagery dated in 2002 already shows taxiways, auxiliary runway and entrances in place.


PLA-NAF Guiping Mengshu AB / Guangzhou MR


Base Location: 23°19'58.33"N / 110° 0'31.93"E
Base Primary R/W: 09/27
Base Primary R/W Length: 10,200 ft
Base Status / Tenant: 3rd BD / 8th AR (H-6D, HU-6D)

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This base has a typical H-6 rated primary runway, and two 33 metre underground hangar entrances at the northeastern corner of the runway system, the easternmost of which has a taxiway in a poor state of repair. The base hosts a squadron of Badger aerial refuelling tankers.


PLA-AF Leng Shui Chi AB / Guangzhou MR


Base Location: 31° 6'24.33"N / 112°24'9.09"E
Base Primary R/W: 04/22
Base Primary R/W Length: 7,200 ft
Base Auxiliary R/W: 16/34
Base Auxiliary R/W Length: 6,900 ft
Base Status / Tenant: Unknown

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This base is of an unusual configuration, with the auxiliary runway almost as large as the primary runway and clearly viable for takeoffs and landings. This, and the 15 - 20 metre wide taxiways and entrances suggest this base was constructed for H-5 bomber operations. Poor image resolution precludes an exact assessment of the base status, but a hangar length of at least 400 metres is evident.


PLA-AF Shaodong AB / Guangzhou MR


Base Location:  27°13'32.16"N / 111°40'10.54"E
Base Primary R/W: 05/23
Base Primary R/W Length: 9,500 ft
Base Status / Tenant: 8th BD H-6A/E

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Shaodong is a H-6 Badger base, which includes an underground hangar with two 33 metre entrances, at the end of a convoluted 3 km taxiway to the southwest of the base.


PLA-AF Shaoguan AB / Guangzhou MR


Base Location:   24°58'54.46"N / 113°25'18.19"E
Base Primary R/W: 15/33
Base Primary R/W Length: 7,100 ft
Base Status / Tenant: 9th FD J-6

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The Shaoguan airbase was constructed to house interceptors, and is equipped with two 12 metre hangar entrances, which yield an estimated tunnel length of ~750 metres.



A 1962 KH-4 Corona LEO image of the Shaoguan interceptor base during construction. To the top of the image is the hill to the North of the runway system, with the taxiways visible, and runup bays occupied by construction sheds (US DoD via FAS).


PLA-AF Wudangshan AB / Guangzhou MR


Base Location: 32°23'21.74"N / 111°41'43.57"E
Base Primary R/W: 17/35
Base Primary R/W Length: 10,400 ft
Base Status / Tenant: 27th FD J-7  / Unknown AR

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The Wundangshan base is unusual, in the sense that it has a large primary runway of the type commonly seen at bomber bases. There is evidence of one incomplete 15 metre hangar entrance, and other, under a foliage canopy which may or may not have been completed. The base currently hosts a J-7 unit.


PLA-AF Yaotian AB / Guangzhou MR


Base Location: 26°31'48.26"N / 112°50'38.01"E
Base Primary R/W: 04/22
Base Primary R/W Length: 9,500 ft
Base Status / Tenant: 8th BD H-6A/E, H-6U, H-6H; 2nd BD PLAN HZ-5

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Yaotian is a satellite airfield which is not connected by a taxiway to the Leiyang / Hsin Shi primary base, which hosts an Air Regiment of H-6 Badgers. The two airfields are separated by a river. The underground hangar has two 33 metre entrances.



CHINAUGFJINAN

Jinan MR Underground Airbases, Geographical Placement [Click to enlarge].

PLA-AF Guodu AB / Jinan MR


Base Location:
Base Primary R/W: 12/30
Base Primary R/W Length: 7,100 ft
Base Auxiliary R/W: 04/22
Base Auxiliary R/W Length: 6,300 ft
Base Status / Tenant: Unknown

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The Guodu base was constructed as a H-5 bomber base, with an underground hangar equipped with two 20 metre entrances, and an internal length of at least 500 metres. The auxiliary runway is of sufficient length to permit both landings and takeoffs, with the entrances difficult to attack in the canyon between two mountains. There is no evidence of recent operational activity, and this base is not equipped with typical administrative and garrison buildings.


PLA-AF Jining AB / Jinan MR


Base Location: 35°17'32.87"N / 116°20'48.66"E
Base Primary R/W: 08/26
Base Primary R/W Length: 9,500 ft
Base Status / Tenant: 19th FD / 55th AR (J-11, Su-27SK, Su-27UBK); Unknown BD H-6









Jining was constructed as a bomber base, with a dual 40 metre entrance underground hangar north of the main apron area. It continues to host H-6 Badgers, but also the 9th Air Regiment of  7th Fight Division Flankers.


PLA-AF Jiyuan AB / Jinan MR


Base Location: 35° 7'11.06"N / 112°36'31.44"E
Base Primary R/W: 08/26
Base Primary R/W Length: 9,100 ft
Base Auxiliary R/W: 10/28
Base Auxiliary R/W Length: 6,500 ft
Base Status / Tenant: Unknown

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Jiyuan was constructed as a H-6 bomber base, but includes an auxiliary runway. An underground hangar is located north of the runway system, and has two 33 metre entrances, one of which is in a state of disrepair, as is the auxiliary runway.


PLA-AF Luyang / Ranghe Zhen AB / Jinan MR


Base Location: 33°41'4.62"N / 112°53'26.89"E
Base Primary R/W: 10/28
Base Primary R/W Length: 7,200 ft
Base Auxiliary R/W: 04/22
Base Auxiliary R/W Length: 5,200 ft
Base Status / Tenant: Storage facility / Museum

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The Luyang site is an unusual configuration, employing a conventional fighter primary and auxiliary runway, with an underground hangar. The hangar has a pair of eastern 15 metre entrances connected to the auxiliary runway. The western side has a single 22 metre entrance., and a 35 metre entrance to a blind tunnel hangar. An incomplete excavation for another 22 m entrance is south of the paired eastern entrances. It is likely this site was intended to initially host H-6, H-5 and J-6, J-7 aircraft. Detail imagery of blast doors is available in Annex C.3.


PLA-AF Neixiang  AB / Jinan MR


Base Location:  32°58'21.77"N / 111°53'7.01"E
Base Primary R/W: 17/35
Base Primary R/W Length: 9,100 ft
Base Status / Tenant: Unknown

PLA-Neixang-AB-UGH-2011-1









This base, located at the southern boundary of the Jinang MR, show clears evidence of an underground hangar system to the West of the runway system, with an estimated tunnel length of ~800 metres under the mountain directly to the West. The smaller mountain to the NW of the runway system may also contain an underground hangar, although poor image resolution precludes a conclusive identification at this time. The wide 30 metre taxiways, 9,100 ft main runway, and characteristic apron pattern indicate this base was constructed for H-6 Badgers.


PLA-AF Yantai Southwest  AB / Jinan MR


Base Location: 37°24'3.03"N / 121°22'2.52"E
Base Primary R/W: 04/22
Base Primary R/W Length: 8,800 ft
Base Status / Tenant: 5th AD F/GAD Q-5

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The Yantai SW base is an atypical fighter base, which incorporates both an underground hangar and no less than 25 revetments with surrounding berms, each protecting a pair of Q-5 Fantans. The underground hangar is located a distance of 2.7 kilometres west of the runway system, and is accessed via a 200 metre road bridge crossing a canal. Both hangar entrances are 15 metres wide.


PLA-AF Yidu/Chijian  AB / Jinan MR


Base Location: 36°35'35.72"N / 118°31'43.69"E
Base Primary R/W: 18/36
Base Primary R/W Length: N/A ft
Base Status / Tenant: Abandoned / Derelict







Yida is former H-5 Beagle base. The runway is covered with warehouse structures, the site is no longer usable for flight operations.



CHINAUGFCHENGDU

Chengdu MR Underground Airbases, Geographical Placement [Click to enlarge].



PLA-AF Guiyang AB / Chengdu MR


Base Location: 26°24'30.27"N / 106°32'5.62"E
Base Primary R/W: 17/35
Base Primary R/W Length: 8,200 ft
Base Auxiliary R/W: 02/20
Base Auxiliary R/W Length: 6,600 ft
Base Status / Tenant: XXth FD / YYth AR

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Guiyang is a fighter base with an auxiliary runway, and an underground hangar south of the primary runway system. Four 15 metre entrances provide access to the hangar.


PLA-AF Wenshan/Pinquan  AB / Chengdu MR


Base Location:  23°42'55.90"N / 103°49'31.40"E
Base Primary R/W: 14/32
Base Primary R/W Length: 8,000 ft
Base Status / Tenant: Unknown

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This base shows characteristic construction features for an underground hangar, including a prominent 15 - 20 metre wide taxiway around the base of the hill to the North of the runway system, and four likely entrances on the North side of the hill. This presents as a similar arrangement to Luyang AB and Guiyang AB, and has been used for H-5 and mixed basing arrangments. Entrance placements indicate ~400 to ~800 metres of internal length. Poor image resolution precludes an assessment of base status.




The abundance of mountainous and hilly terrain across the eastern Military Regions of China created many opportunities to site airfields with underground hangars. The compact Chengdu J-10 Sino-canard fighter will fill all three hangar types (via Chinese Internet).


Annex B - Underground Hangar Capacity Estimation


Estimating the capacity of the PLA's network of underground hangars presents some challenges, in the absence of published floorplans. While the cross-section of the entry tunnels can be accurately estimated from imagery, absence of knowledge about internal layouts, especially if the hangar comprises multiple branching or parallel tunnels, presents a high risk of underestimating internal capacity.

The small number of available images, and publicly accessible Datangshan interior suggest that a simple arrangement may be commonly employed, connecting entrances with a single tunnel of constant cross-section, following an |-, L-, U- or S-shaped pattern to connect the pair of entrances.

To test this hypothesis, we estimated tunnel lengths for all of the sites listed in Table B.1, routing the tunnel under the peak of the hill or mountain. Where the geometry permitted multiple footprints consistent with the hypothesis, we looked at best case (longest) and worst case (shortest) case paths.

Assuming a future PLA Orbat comprising a mix of H-6H/M/K/U, J-11A/B/Su-30MKK/MK2, J-20 and J-10, we postulated reasonable placements for all types, given prevailing tunnel widths.

While the results for the J-11A/B/Su-30MKK/MK2 and J-20 do not correlate well with any arrangement employing the H-5 Beagle, given the fundamentally different platforms of the newer swept wing types, this should not be a surprise.

The results for the H-6 Badger, listed in Table B.1, typically fall into integer multiples of 12 aircraft squadrons, with some spares. The aggregate figure is ~140 aircraft, a number which  is greater than the ~120 which repeatedly appears in unclassified assessments of the total strength of the PLA's H-6 fleet. Prima facie this would suggest that the PLA maintains underground hangar capacity for the whole of its H-6 Badger fleet. An additional large hangar complex at Leng Shui Chi AB was excluded due to uncertainties about status and capacity.

The underground hangars built for the legacy cloned MiG fighters yielded interesting results for the J-10, despite its different planform and slightly larger footprint. Most of the underground hangars yielded numbers which were, yet again, integer multiples of 12 aircraft squadrons, with some spares. The aggregate figure is ~600 up to ~800 aircraft, which means that these underground hangars could protect around 3/4 of the often cited target production quantity for PLA-AF/NAF J-10A/B/S fighters.

At this time the Flanker is the primary air superiority and deep strike fighter of both the PLA-AF and PLA-NAF. As a result, it is reasonable to consider how many Flankers could be accommodated in H-5 sized underground hangars. The resulting ~600 aircraft sits at the upper bound of previously cited numbers planned for the PLA Flanker fleet, and is well above the current total deployed in operational units.

The J-20 will likely become the spearhead of the PLA-AF's TACAIR fleet, and is thus a high value asset worthy of considerable protection from counter-air strikes. The extant H-5 sized underground hangars could accommodate ~500 J-20 aircraft, assuming the aircraft's cardinal dimensions and planform do not change significantly during development.

The estimation method employed is inherently conservative, and will underestimate actual capacity, as in the absence of data, no allowance could be made for branching tunnel capacity.



Comparative area occupancy for PLA underground hangars, for Badger and Flanker variants. Former Badger bases will be able to accommodate significant numbers of J-11A/B and Su-30MKK/MK2 Flanker aircraft. An underground hangar sized to fit a dozen H-6 Badgers could comfortably fit an Air Regiment of 36+ Flankers (C. Kopp).

Hangars constructed with a 20 - 22 metre entrance/tunnel width to accommodate the H-5 Beagle provide an ideal environment for hangaring the J-11A/B/Su-27SK Flanker B and Su-30MKK/MK2 Flanker G. An example arrangement is a slanted row with aircraft spaced 14 metres apart (C. Kopp).

Hangars constructed with a 20 - 22 metre entrance/tunnel width to accommodate the H-5 Beagle would also be compatible with the new J-20, despite its greater length compared to the Flankers. An example arrangement is a slanted row with aircraft spaced 19 metres apart (C. Kopp).


Hangars constructed with a 12 - 15 metre entrance/tunnel width to accommodate the J-4 Fagot, J-5 Fresco, J-6 Farmer and J-7 Fishbed are less than optimal for stowing later types such as the J-8 Finback and J-10 series. The J-10 can be stowed nose to tail, or with ~20% higher packing density, stowed slanted (C. Kopp).

Table B.1
7 x H-6 Badger Underground Hangars
PLA Base
Lin / Arc Distance
Width
H-6
Notes
PLA-AF Wenshui AB / Beijing MR 600 40 16

PLA-NAF Foluo Northeast AB / Guangzhou MR 735
40
20

PLA-NAF Guiping Mengshu AB / Guangzhou MR 820 - 973
33
22 - 27

PLA-AF Shaodong AB / Guangzhou MR 360 - 430
33
10 - 12

PLA-AF Yaotian AB / Guangzhou MR 650 - 950
33
18

PLA-AF Jining AB / Jinan MR 1,000
40
27

PLA-AF Jiyuan AB / Jinan MR 900
33
25

Nett

138 - 145

H-6 Min Distance 36 m Nose-Tail














14 x H-5 Beagle Underground Hangars
PLA Base
Lin / Arc Distance
Width
J-20
J-11
Notes
PLA-AF Jichang AB / Shenyang MR 350 + 630 = 980
22
51
70
Dual UGH
PLA-AF Lihue AB / Shenyang MR 800
22
57
42

PLA-AF Nangangzi AB / Shenyang MR 800 22 57 42
PLA-AF Pingquan AB / Shenyang MR ~1,000
22
52
71
Triple Entry UGH
PLA-AF Chen-Chuan AB / Beijing MR 600 22 31 42
PLA-AF Yongning AB / Beijing MR 670
22
35
47

PLA-AF Yinchuan / Xincheng AB / Lanzhou MR 400
22
21
28
Dual UGH Mixed
PLA-AF Changzing AB / Nanjing MR 600
22
31
42

PLA-NAF Feidong AB / Nanjing MR 770
22
40
55

PLA-AF Suzhou West AB / Nanjing MR 900
22
47
64

PLA-AF Taihe AB / Nanjing MR 600
22
31
42

PLA-NAF Yiwu AB / Nanjing MR 750
22
39
53

PLA-AF Guodu AB / Jinan MR ~500 22 26 35
PLA-AF Luyang AB / Jinan MR ~500
22
26
35
Dual UGH Mixed
Nett


544
668

J-11 Min Distance 14 m Slant






J-20 Min Distance 19 m Slant















17 x J-4 Fagot / Q-5 Fantan / J-6 Farmer / J-7 Fishbed Underground Hangars
PLA Base
Lin / Arc Distance
Width
J-10
Notes
PLA-AF Chifeng AB / Shenyang MR 650
13
40

PLA-AF Fuxin AB / Shenyang MR 450
15
28

PLA-AF Jinzhou Xiaolingzi AB / Shenyang MR 280
15
17

PLA-AF Fengning AB / Beijing MR 600
15
37

PLA-AF Hohhot AB / Beijing MR ~700
15
43

PLA-AF Jizhuang AB / Beijing MR ~700 15 43
PLA-AF Zhangjiakou AB / Beijing MR 400 + 400 = ~800
15
50
Dual UGH
PLA-AF Zunhua AB / Beijing MR 400 - 1,000
15
25 - 60

PLA-AF Urumqi South AB / Lanzhou MR 900
15
56

PLA-AF Yinchuan / Xincheng AB / Lanzhou MR 460 - 530
15
28 - 33
Dual UGH Mixed
PLA-AF Anqing AB (An Ching) / Nanjing MR 600
15
37

PLA-NAF Daishan Island AB / Nanjing MR 600
13
37
Derelict
PLA-AF Guiyang AB / Nanjing MR 500 + 400 = 900
15
60
Dual UGH
PLA-AF Wudangshan AB / Guangzhou MR ~500
15
31
UNK
PLA-AF Shaoguan AB / Guangzhou MR ~750
12
46

PLA-AF Luyang AB / Jinan MR ~700
15
43
Dual UGH Mixed
PLA-AF Yantai Southwest  AB / Jinan MR ~1,000
15
62

Nett

683 - 723

J-10 Min Distance 16 m Nose-Tail















Three ABs have been excluded from the capacity analysis due to poor image resolution precluding conclusive assessments of status and entrance widths. These are PLA-AF Leng Shui Chi AB / Guangzhou MR, PLA-AF Neixiang  AB / Jinan MR, and PLA-AF Wenshan/Pinquan  AB / Chengdu MR.


Annex C - PLA Airbase Design and Construction in Detail


PLA airbase design is standardised to an extent not observed in NATO nations, or former Warpac nations. This Annex will provide additional reference material detailing the external and internal design features of these standard base designs.


Annex C.1 - General Site Layout and Design





A characteristic design feature of most PLA airbases is the use of large alert aprons at either end of the parallel main runway/taxiway system. Above J-6 Farmers on the alert apron, below H-5 Beagles (via Chinese Internet).





PLA airbases without underground hangars usually have a central apron, adjacent to hangars used for engineering work on the aircraft and systems. This base, hosting Q-5 Fantan close air support aircraft, displays camouflaged structures, a common feature on Warpac style bases with revetted dispersal pads (via Chinese Internet).



Lightweight aircraft shelters have been installed on the main aprons of many PLA airbases. Above, below: two types are used most commonly. They provide protection against weather and overhead ISR assets, but not against PGMs  (Chinese Internet).






China is the only nation, globally, able to protect its aerial tanker fleet by concealment in underground hangars. The Xian H-6 Badger remains in production as a cruise missile carrier and tanker. It is a reverse engineered Tu-16, itself a descendant of the Boeing B-29, the Tu-16 developed initially to compete against the British V-bombers (Zhenguan Studio, © 2010 Air Power Australia).

SHANTOUNEHAS

Shantou NE AB hosts the PLAAF 24th AR of the 9th FD, operating the J-10A. It is an excellent example of a “classic” Warsaw Pact pattern base with revetted dispersal areas, which have been hardened by the installation of HAS on previously revetted dispersal pads. Survivability of hangared aircraft will be determined by the ability of the shelters to resist penetrating munitions like the GBU-39/B (S. O'Connor).

LONGTIANHASANDREVET

Longtian AB is another excellent example of a “classic” Warsaw Pact pattern base with revetted dispersal areas, which have been hardened by the installation of HAS. Longtian and a number of other bases have camouflage paint applied to the taxiways and ramps which access the HAS, arguably a futile effort, given that the location has been surveilled by satellite since its initial construction, evidenced by the KH-4 image below (S. O'Connor, US DoD).




FEIDONGOVERVIEW

Feidong AB hosts the PLANAF 10th AR of the 4th FD, operating the maritime strike Su-30MK2 Flanker G. Feidong is  the archetypal superhardened base, with an underground hangar and auxiliary runway (S. O'Connor).

FEIDONGAIRFIELD

Detail of the Feidong AB main runway, alert ramps and main apron with lightweight aircraft shelters. The lightweight shelters offer protection from the elements but are not hardened against penetrating munitions. (S. O'Connor).

FEIDONGUGHAREA

Detail of the Feidong AB auxiliary runway, taxiway system, and underground hangar. Many bases with underground hangars include turnaround points or aprons along the auxiliary runway or taxiway to permit takeoffs while returning aircraft are being towed back to the underground hangar. While the auxiliary runway is long enough for a FLANKER-series aircraft to land on it, there is insufficient vertical clearance for go-arounds (S. O'Connor).

FEIDONGUGHENTR

Detail of the Feidong AB underground hangar entrance and access taxiway. Many bases with underground hangars display localised patches of debris and dirt on the taxiways, mostly likely the result of mudslides or runoff from the mountainside during heavy precipitation, the latter a common occurrence in eastern China. Many bases also show active construction work on entry ramps or taxiways, indicating maintenance efforts on these surfaces (S. O'Connor).

FEIDONGUGHEXT

Detail of the Feidong AB underground hangar exit and ramp, start of auxiliary runway,  garrison buildings, and POL bulk storage facility. The latter is unusual in that it is fully exposed and  may only be used for intermediate storage prior to transfer to underground storage in a contingency  (S. O'Connor).

FEIDONG3D

Detail of the Feidong AB underground hangar area in synthetic three dimensional rendering. The reshaping of the hillside near the entrance may reflect attempts to control runoff and mudslides which might otherwise impair operations. The purpose of the water catchment is unclear, and may simply be used to support agricultural irrigation in proximity to the hangar. It has been present since 2003 (S. O'Connor).


Annex C.2 - Hangar Internal Design


Interior imagery of PLA underground hangars is generally scarce, and usually of poor quality, most likely intentionally so. The PLA has nothing to gain by propagating such material, other than to provide insights to potential opponents on the weaknesses of the designs in use.



Interior view of concertina inner door arrangement in  the 14 metre wide underground hangar system at Gjadër / Lezhë-Zadrima AB in Albania. In the foreground a Chinese supplied J-6 Farmer of the Albanian Air Force, with NR-23 guns removed (Courtesy of Chris Lofting).



Exterior view of open convex external blast door arrangement in the 14 metre wide underground hangar system at Gjadër / Lezhë-Zadrima AB in Albania. The primary convex external blast doors employ a reinforcing internal structural framework to transfer overpressure loads into the outer frame. The upper external blast door is closed (Courtesy of Holger Müller@MiG-21.de).



Another exterior view of open convex external blast door arrangement in the 14 metre wide underground hangar system at Gjadër / Lezhë-Zadrima AB in Albania. The upper door is hinged on the right hand side of the door. The concrete arch over the main entrance is a characteristic feature observed at Chinese sites. In the foreground a Chinese supplied J-6 Farmer of the Albanian Air Force (Author unknown).

The alternative to imagery of sites in China proper is to explore sites in other nations, built to the same design rules and specifications. A number of client states procured significant numbers of Chinese aircraft since the 1960s, but only the DPRK and the former Hoxha regime in Albania also imported design data and constructed airfields with underground hangars to the PLA specification. Albania received ongoing aid from China until the late 1970s, when the relationship collapsed.



14 m underground hangar external blast door geometry (© 2011, C. Kopp).




14 m underground hangar entrance and inner door geometry (© 2011, C. Kopp).

Two excellent collections of high quality imagery of three Albanian underground hangars at Tirana-Rinas AB, Gjadër / Lezhë-Zadrima AB and Kuçovë AB, have been produced by aviation photographers Chris Lofting and Holger Müller, and are available, respectively, at Airliners.net [Click Here to view the full archive] and MiG-21.de [Click Here to view the full archive].



Main tunnel of the 14 metre wide underground hangar at Gjadër / Lezhë-Zadrima AB in Albania. In the foreground Chinese supplied J-6 Farmers, with pitot probes in characteristic stowed position. The area to the right is cleared for vehicle movements  (Courtesy of Chris Lofting).




Main tunnel of the 14 metre wide underground hangar at Gjadër / Lezhë-Zadrima AB in Albania. The design is a linear segmented arrangement. Note the sheetmetal cladding (Courtesy of Chris Lofting).



Branching short tunnel in the 14 metre wide underground hangar at Gjadër / Lezhë-Zadrima AB in Albania. This example is being used for maintenance of a J-7 Fishbed, in this instance involving an engine change (Courtesy of Chris Lofting).



Another view of the same branching tunnel in the 14 metre wide underground hangar system at Gjadër / Lezhë-Zadrima AB in Albania (Courtesy of Holger Müller@MiG-21.de).



Primary tunnel of the 14 metre wide underground hangar system at Gjadër / Lezhë-Zadrima AB in Albania (Courtesy of Chris Lofting).



Primary tunnel in the 14 metre wide underground hangar system at Gjadër / Lezhë-Zadrima AB in Albania, viewed closer to the bend in the tunnel. The J-7 Fishbed aircraft are an early configuration (Courtesy of Holger Müller@MiG-21.de).



Branching short tunnel in the 12 metre wide underground hangar at Tirana-Rinas AB in Albania. This example  appears to be ~60 metres in length, sufficient to hangar four J-6 Farmers (Courtesy of Chris Lofting).

A number of very useful observations can be made from this imagery:
  1. Layout: The primary tunnel connecting the paired main entrances typically comprises linear segments, joined by gently curved sections. This is one of the possible strategies for the layout, and arguably the easiest to construct;
  2. Layout: Branching blind tunnels of ~60 metres length are employed, with entrances from the primary tunnel. These are used, in the Albanian tunnels, to either perform deeper maintenance on single aircraft, or to hangar multiple aircraft, parked nose to tail. The blind tunnel junctions with the primary tunnel are at a right angle, in the available imagery;
  3. Geometry: Two different tunnel cross-sections are employed. One is a ~12 metre wide simple catenary section, down to the tunnel floor, used at the Tirana-Rinas site. The other is a ~14 metre wide compound cross section, with  ~3.4 m high vertical walls and a catenary section upper lobe, with an overall internal height of ~6.3 metres. The latter is used at the Gjadër / Lezhë-Zadrima AB and Kuçovë AB sites;
  4. Entrances and Inner Doors: The primary tunnel entrances at Gjadër / Lezhë-Zadrima AB and Kuçovë AB are through an inverted T shaped main door arrangement. Hinged external blast doors are used, with a multiple segment horizontally opening steel concertina inner door, supplemented by a smaller vertically opening steel concertina door used to seal the  slit aperture for the aircraft's vertical tail (refer illustrations above). It is unclear whether this arrangement would seal well enough for operation in an NBC environment, although maintenance of positive pressure inside the hangar could alleviate seal problems when the inner door is closed. The inner doors are certainly used to protect against adverse weather;
  5. External Blast Doors: The left and right main and upper hinged blast doors are  externally convex, where the curvature is across the shorter dimension. Construction appears to be steel. Available imagery suggests either a circular section or catenary curvature, intended to transfer overpressure loads into the outer frame of the blast doors. The doors swing outward on hinges, and the inner side of the door aligns exactly with the left and right inner tunnel walls. The blast doors and upper concrete wall structure are located about 7 metres from the hillside entrance, to protect the open blast doors;
  6. Inner Blast Doors: The Gjadër / Lezhë-Zadrima AB and Kuçovë AB a second pair of hinged blast doors in a plenum chamber arrangement as depicted by Roland Büchler (below). This forms a defacto airlock arrangement at either end of the plenum chamber.
  7. Internal Construction: The internal walls of the tunnels are lined with reinforced concrete. The construction method would appear to involve setting up a frame, with wooden planks to form a mold, and pouring the concrete in short segments of ~2  to 3 metres. The ~12 m Tirana-Rinas  AB tunnels show contiguous pouring of these segments. The ~14 metre Gjadër / Lezhë-Zadrima AB and Kuçovë AB have exposed steel I-beam inner webs at intervals of ~3 metres in linear tunnel segments, and as little as ~1 metre in tunnel bends. These are likely to be reinforcement for the final structure, but also used to support the formwork during construction. Portions of the Gjadër / Lezhë-Zadrima AB tunnel show evidence of the molds sagging during the pouring of the concrete.
  8. Drainage: Water seepage is clearly evident in the joins between segments in the tunnel liner, in sufficient quantities to see pooling on the tunnel floors at both Gjadër / Lezhë-Zadrima AB and Kuçovë AB;
  9. Surface Finishing: Portions of the tunnel walls at Gjadër / Lezhë-Zadrima AB are clad with white  or light coloured enameled sheetmetal, also observed in PLA tunnels; other tunnel walls at Gjadër / Lezhë-Zadrima AB and Kuçovë AB are either unfinished, or smoothly finished. The possible intent of the sheetmetal liner is to improve tunnel illumination, but possibly also to improve VHF radio propagation along the tunnel, or to provide a utilities corridor;
  10. Utilisation: The 14 metre tunnel floors are divided by a white marking line, with ~10 metres along one wall employed for aircraft storage, and the remaining ~4 metres clear for vehicular movements along the length of the tunnel; PLA tunnels appear to use a similar arrangement.
The 14 metre tunnel design is very common in Chinese installations and is likely much newer by design than the 12 metre tunnel design. The interior volume of the former is generous for the aircraft sizes employed, and considerable freedom of movement is available for refuelling truck, weapons dollie and other vehicular movements required to sustain operations.

Layout diagrams for the Gjadër / Lezhë-Zadrima AB and Kuçovë AB sites have been produced by Roland Büchler, following a site visit. Both sites employ a horseshoe linear segmented arrangement, as suggested by photographic evidence.



The Gjadër / Lezhë-Zadrima AB (above) and Kuçovë AB (below) sites employ horseshoe / linear segmented arrangement (© Roland Büchler).



The likely operating cycle is that aircraft are always towed into one entrance, and launched from the other. Aircraft returning from sorties would be placed at the beginning of a queue, and flow down the tunnel receiving, progressively, flightline maintenance, fuel and munitions loads, as they approach the other end of the tunnel. Aircraft requiring more time consuming maintenance would be placed into branching tunnels not to stall the servicing, fuelling and arming “pipeline” as it flows down the tunnel.

The entrance external blast door design observed in Albania is similar to some known images of Chinese hangar blast doors, but different from others, suggesting a number of different designs are in use. The Albanian blast door design is clearly designed to survive overpressure events and high velocity shrapnel and spall. It is unlikely that the  single blast door design is robust enough to stop a modern penetrating munition such as the GBU-39/B or BLU-116/B, and may well reflect the chronological age of the design, constructed in the era of “dumb” munitions. With inner and outer blast doors closed, the inner door would likely stop smaller munitions which may have penetrated the outer door.

The entrance inner concertina door design observed in these tunnels is not especially robust in a PGM threat environment. A penetrating munition which has passed through the external  and inner blast doors would likely punch through the inner  concetina door panels, or join between the panels, and even if the munition does not penetrate inside the hangar, it would likely produce sufficient twist in  one or two door panels to preclude the concertina mechanism from working, effectively jamming the door shut.


Annex C.3 - Hangar External Blast Door Designs


Available open source imagery indicates that a number of different blast door arrangements are employed, with at least two types employed for “MiG-sized” hangars, at least one for “Beagle-sized” hangars and one for “Badger-sized” hangars. These are detailed below. Imagery courtesy of Roland Büchler.



The Luyan / Ranghe-Zhen AB site has an accessible “Badger-sized” hangar with a sliding, segmented external blast door arrangement. Tunnels normal to the entrance have been excavated to provide stowage for the doors when open  (Chinese Internet).



Above, below: detail of Luyan / Ranghe-Zhen AB “Badger-sized” external blast door arrangement (Chinese Internet).







Luyan / Ranghe-Zhen AB (above) and Zhangjiakou AB (below) “Beagle-sized” external blast door arrangement. These two part sliding blast doors retract into normal tunnels left and right of the entrance.





Zhangjiakou AB “Beagle-sized” external blast doors retracted (Chinese Internet).



Satellite imagery shows this abandoned “Beagle-sized”  hangar entrance at the Luyan / Ranghe-Zhen AB site, on the eastern face of the mountain, south of the paired “MiG-sized” hangar entrances. A brick wall has been constructed to block the entrance (Chinese Internet).



Above, below: Hinged blast doors at an unidentified PLA “MiG-sized” hangar (Chinese Internet).





Open hinged blast doors at an unidentified PLA “MiG-sized” hangar. Note the camouflage netting suspeded above the entrance (Chinese Internet).



The Luyan / Ranghe-Zhen AB site has a pair of “MiG-sized” hangar entrances with a hinged external blast door arrangement, on the eastern face of the mountain (Chinese Internet).


Hinged blast doors using an alternate lightweight configuration at an unidentified PLA “MiG-sized” hangar (Chinese Internet).





Air Power Australia Analyses  ISSN   1832-2433




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