Hardened Aircraft Shelters

A pair of Hardened Aircraft Shelters (HAS), buildings 4109 and 4110, were constructed around 1983 by the US Air Force at Alconbury Airfield. These buildings are unique as they are the only examples of this type of shelter found anywhere in Europe, with a total of 13 such shelters built at Alconbury. They were specifically designed to accommodate the large wingspan (31.39 metres) of U2/TR1 reconnaissance aircraft.

The shelters are steel-framed with concrete panelling and are clad in corrugated metal, painted in standard NATO dull brown. They have a rectangular plan, with a single-storey pedestrian entrance on the left-hand side. The distinctive convex roof is punctuated by T-shaped roof ventilators. The massive rolling steel and concrete doors, mounted on runners, are supported by a framework of steel girders designed to distribute the weight evenly across the runners.

The interiors are lined with corrugated metal. Many original features remain, including the reinforced concrete floors, air filtration plant, ducting, lighting, and electrical switch gear. Towards the rear of the shelters, a concrete platform and crew room at an upper level are accessible via a metal staircase. Jet efflux was vented through an opening to a blast deflector fence.

Alconbury airfield was first acquired in 1938 and used by the RAF during the Second World War. It was later reactivated in 1953 for the US 3rd Air Force, and from 1959 served as a crucial Cold War base for reconnaissance squadrons. The construction of the 13 extra-wide HAS occurred in 1983 when U2/TR-1 aircraft were permanently based at the site, along with a squadron headquarters, avionics building and new aprons and taxiways. Flying ceased in 1995 and the base has subsequently been put to commercial uses.

The HAS are considered to be rare and significant examples of military architecture, reflecting the Cold War era’s tensions and the deployment of U2/TR1 aircraft. They possess considerable group value when considered alongside the airfield’s other Cold War-era buildings, particularly the Avionics building.