 90 Squadron flew its first operational mission on 8 July 1941, when three Fortresses set off from RAF Polebrook to attack Wilhelmshaven (although only two of them actually managed to bomb the target).The squadron typically flew small formations of Fortresses in high altitude daylight attacks, taking part in a large scale attack on the at Brest, France on 24 July.Three Fortresses attacked were to attack from , with the objective of drawing German fighters away from 18 Handley Page Hampdens attacking at lower altitudes.