The Halifax became the second of the new generation of four-engine heavy bombers to enter service with RAF Bomber Command in the Second World War. It flew its first offensive operation in March 1941 and by 1944 it had become the exclusive equipment for Bomber Command's 4 Group and 6 (Canadian) Group, as well as being used in smaller numbers by 100 (Bomber Support) Group. The Halifax flew on virtually all the main raids of the night offensive between 1942 and 1945 and the last occasion when Bomber Command Halifaxes operated in strength against the enemy was on 25 April 1945.