Hardened aircraft shelter

Hardened aircraft shelter at RAF Bruggen, 1981

A hardened aircraft shelters (HAS) or protective aircraft shelter (PAS) is a reinforced hangar to house and protect military aircraft from enemy attack. Cost considerations and building practicalities limit their use to fighter size aircraft.

Background

HASs are a passive defence measure (i.e., they limit the effect of an attack, as opposed to active defences; e.g., surface-to-air missiles) which aim to prevent or at least degrade enemy attacks. The widespread adoption of hardened aircraft shelters can be traced back to lessons learned from Operation Focus; in the 1967 Arab-Israeli Six-Day War when the Israeli Air Force destroyed the unprotected Egyptian Air Force, at the time the largest and most advanced air force in the Arab world, at its airbases.

An F-16 being towed into a HAS at Volkel Air Base

As with many military items, whether structures, tanks or aircraft, its most prolific use was during the Cold War. NATO and Warsaw Pact countries built hundreds of HASs across Europe. In this context hardened aircraft shelters were built to protect aircraft from conventional attacks as well as nuclear, chemical and biological strikes. NATO shelters, built to standard designs across the continent, were designed to withstand a direct hit by a 500 lb (226 kg) bomb, or a near miss by a larger one (i.e., 1,000 lb+). In theory HASs were also built to protect aircraft in a nuclear strike; however, the effect of such an attack on airfield taxiways, runways, support facilities and personnel would have made any retaliatory mission extremely difficult and subsequent return and rearming almost impossible.

In the post-cold war era, the value of the HAS concept was further eroded by the introduction of precision-guided munitions. Iraq's HAS hangars were built to a standard somewhat higher than NATO or Warsaw Pact shelters, but nevertheless proved almost useless during the Gulf War. Early attempts to defeat them typically used a "one-two punch" using a TV-guided missile to blast open the doors, followed by bombs tossed in the front. US efforts soon turned to simply dropping a 2,000 lb laser guided bomb on the top, which would easily penetrate the roof and explode within. With that being said, however, NATO hangars would still remain useful against the forces of any enemy as might conceivably engage Europe in an armed conflict in the short term (whose capabilities generally lack precision guidance systems needed to defeat the defensive shield such hangars offer).

Advantages

Inside a PAS, showing a Weapons Storage and Security System vault in raised position holding a B61 nuclear bomb

Disadvantages

Two reinforced hangars showing the effects of Coalition bombing during Operation Desert Storm, 1991. These Kuwaiti shelters were built by the French and used by Iraqi forces during the conflict. Picture is of Ahmed Al Jaber Air Base - Kuwait.

Alternatives

Deployable shelters
Kevlar lined deployable shelters could protect aircraft from bomblets (a common anti-airfield weapon). However this would provide no protection from PGMs.
Dispersal at bases
Wider dispersal (distance between aircraft) at airfields would decrease the vulnerability of aircraft. This would also force an enemy to increase the number of attacking aircraft greatly, or spend more time over the target. Either way the effect of airfield defences would take a heavy toll on the aggressor. However like HAS, dispersal can be expensive, requiring massive construction of hardstanding. Defense against enemy special forces is also more difficult.
Dispersal between bases
Dispersing aircraft between many bases greatly increases the cost of attacking a given number of aircraft, as measured by the number of attack aircraft required. However, this option similarly increases the defenders' cost of operation and degrades their efficiency.
Dispersal to highway strips
Dispersal of aircraft to highway strips will present the attacker with a multitude of targets which cannot be simultaneously attacked. Survivability is enhanced if the defender also chooses to use mobile tactics, using each highway strip for a limited number of sorties before moving on to another. With penny packets of two to four aircraft at each location, such a tactic increases the difficulty of effective co-ordination, and command and control, it also increases vulnerability to attack from the ground. However, with adequate planning these are not insurmountable problems; for example Sweden, one of the main subscribers to the highway strip doctrine, has a special forces unit, the Flygbasjägare, raised especially to counter the threat of attack by enemy special forces.
Underground hangars
Several air forces have used tunnels dug into a mountainside as underground hangars.

See also

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