Of the operations of the RCAF, the most costly was the strategical bombing offensive against Germany. By October 1942, the RCAF had five bomber squadrons serving with Bomber Command. 425 Squadron was made up of French-Canadians, through English was the language of command for all squadrons. In January 1943, 11 bomber squadrons were formed by transferring all of the Canadians serving in the RAF to RCAF, which become No. 6 Group of Bomber Command under Air Vice-Marshal G.E. Brookes. The air crews serving in 6 Group were based in the Vale of York, requiring longer flights to Germany. The Vale of York was also a region inclined to be foggy and icy in the winter, making take-off and landings dangerous. Furthermore, 6 Group continued to fly obsolete Wellington and Halifax bombers and only received their first Lancaster bombers in August 1943.