Hardened Aircraft Shelters - Definition and Overview

Hardened Aircraft Shelters (HAS) are structures which 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 defense measure, i.e. they limit the effect of an attack, as opposed to active defences (e.g. Surface to Air Missiles or SAMs) which aim to prevent or at least degrade enemy attacks. The widespread adoption of Hardened Aircraft Shelters can be traced back to the 1967 Arab-Israeli Six-Day War when the Israeli Air Force decimated the Egyptian Air Force at its bases, at the time the largest and most advanced air force in the region.

Like many military items; be it a structure, tank or aircraft, its most prolific use was during the Cold War. NATO and Warsaw Pact countries built hundreds of HAS across Europe. In this context Hardened Aircraft Shelters were built to protect aircraft from both 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 500lb (226kg) bomb or a near miss by a larger one (i.e. 1,000lb+). In theory HAS were also built to protect aircraft in a nuclear strike; however the effect of this on airfield taxiways, runways, support facilities and personnel would have made one retaliatory mission extremely difficulty and subsequent return and rearming almost impossible.

Pros

• Reduces vulnerability of aircraft to all but the most accurate precision weaponry
• Combined with active airfield defences increases survivability of defender's aircraft and cost to enemy's forces.
• An alternative option, dispersal of aircraft to many different bases, reduces the efficiency of aircraft at both squadron and air force level.

Cons

• Highly expensive
• Large aircraft can not be easily accommodated in hardened shelters due to their size. Ironically this includes some of the world's air force's most valuable planes, e.g.
  • Airborne Early Warning/AWACS
  • Strategic transports
  • United States Air Force JSTARS
• Time taken for construction requires forward planning regarding most likely combat zones. If a conflict flares up quickly aircraft may be afforded no protection, e.g. in both the Gulf War and 2003 Iraq War many coalition aircraft had only sun shelters, not hardened facilities.
• When first developed the likelihood of a direct hit was minimal, today with Precision-guided munitions (PGMs) and adequate training a direct hit on a HAS is routine. Coalition aircraft destroyed over half of Iraq's HAS during the Gulf War.
• Germany's Luftwaffe has conducted tests to establish the effect of humidity inside a shelter on its aircraft's avionics. Results suggested the higher relative humidity has a higher corrosive effect than outside its shelters. Supply of dry air to avionics compartments has decreased corrosion and increased serviceability.

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 agressor. However like HAS, dispersal can be expensive, requiring massive construction of hardstanding.
• Dispersal between bases
  The dispersal of aircraft between many bases causes an exponential rise in the number of aircraft required to attack a given number of aircraft. However this option creates a similar increase in cost of operation and degredation of efficiency of the defender's aircraft.