With the approach of WW2 the de Havilland Aerodrome at Hatfield went through a major expansion, concentrating on Mosquito production and development. The Company also pioneered the production and development of jet engines led by Major Frank Halford, leading to the Vampire jet fighter. Early commercial aircraft were the Dove and Heron, but the major pioneering program was the Comet, the world’s first commercial jet airliner, which first flew on 27 July 1949 and entered service with BOAC on 2 May 1952. The DH.108 tailless research aircraft based on the Vampire fuselage was used to investigate the effects of the speed of sound, exceeding Mach 1 on 9 September 1948. The de Havilland jet airliner developed through the Trident, which was the first aircraft capable of automatic landing with passengers in all weathers, leading to the BAe 146 Whisper Jet, Britain’s most successful jet airliner. In addition to developing turbojet engines, the Engine Company also developed rocket engines. The Propeller Company developed air-to-air guided missiles and the Blue Streak stage 1 booster space rocket. Other types developed by de Havilland at Hatfield were the Sea Vixen naval strike fighter and the DH 125 Business Jet.