"Royal Air Force Bomber Command, 1939-1941." The crew of Boeing Fortress Mark I, 'WP-G' of No. 90 Squadron RAF, climb out of their aircraft at Polebrook, Northamptonshire, after a daylight attack on the German battlecruiser GNEISENAU docked at Brest, France, which they bombed from 30,000 feet. The crews of the three Fortresses involved found that the Sperry Model 'O' bombsight, with which the Fortresses were equipped, was too inaccurate at that height, and that the Wright Cyclone engines had difficulty in maintaining such an altitude.