During the war, it included a significant proportion of Royal Australian Air Force (or Australian-born RAF) personnel, both aircrews and ground staff, who were concentrated in three "Article XV squadrons": No.

617 Sqn was formed in March 1943, and comprised RAF, RAAF, RCAF/Canadian and RNZAF/New Zealand aircrew personnel, who had been hand-picked from squadrons throughout Bomber Command.

Early in 1942, the Manchester, was replaced by its four-engined variant: the Avro Lancaster, started to equip the group squadrons.

On 17 October 1942, under Operation Robinson, some 86 Lancasters from 5 Group (without fighter escort) flew deep into occupied France to attack the Schneider armaments works at Le Creusot and the associated electrical station at Montchanin.

During the lead-up to D-day, Cochrane was an advocate of low-level marking, to improve accuracy, and lobbied heavily to be allowed to prove the principle operationally.

The special missions included attacks on the German battleship Tirpitz in late 1944 and the use of the Grand Slam against the strategically-important Bielefeld railway viaduct, in March 1945.