Bristol Theseus engine testbed. Location thought to be Radlett. Crashed on 10 April 1951 when three of the turboprops failed. Photo from: Bristol

The Hermes IV prototype first flew from Radlett on 5 September 1948. The aircraft wears a BOAC Speedbird logo similar to the one in photo 634658. Photo from: Bristol

VIP aircraft. Scrapped at Akrotiri, Cyprus in November 1969. Photo from: Imperial War Museums

BOAC sold this aircraft to Aviation Traders in 1948 and it was scrapped two years later. Photo from: Imperial War Museums

Adopted the military serial VX234 in 1953. Photo from: Imperial War Museums

Delivered to No. 35 Squadron at Graveley, Huntingdonshire. HR861 was lost over Nuremberg, August 11 1943. Photo from: Imperial War Museums

The first production Hampden prior to being named by Viscountess Hampden. The name "Hampden" was applied to the nose of the aircraft at the ceremony. L4032 was then delivered the Aircraft and Armament Experimental Establishment. Photo from: Imperial War Museums

The prototype of the Hampden. The production aircraft looked less angular, with the "birdcage" nose replaced by a curved Perspex moulding that incorporated an optically flat bomb aimer's panel. With the aircraft and its tyres in pristine condition, the location is assumed to be Radlett where it was built and made its first flight. However, the museum gave no location for the photo. Photo from: Imperial War Museums

The W.9 helicopter pioneered the NOTAR principle, using coolant air from its DH Gipsy Queen piston engine for torque reaction control. The sole example, PX203, first flew in 1945. It was demonstrated in an air pageant at Southampton on 22 June 1946 too but we believe this is Radlett. It seems to have flown well but work stopped after it crashed. This happened in 1946 according to most sources, though the German Wikipedia gives 20 January 1948. Photo from: Nationaal Archief (Netherlands)

The prototype of the Harrow, an interim heavy bomber, at the HP factory airfield. 100 Harrows equipped five RAF bomber squadrons in the course of 1937, but were replaced by 1940 and subsequently used mostly as transport aircraft. K6933 to G-AFRG in 1939, one of three used in in-flight refuelling trials.