From France's collapse in June 1940 to the German invasion of the USSR in June 1941, Canada supplied Britain with urgently needed food, weapons, and war materials by naval convoys and airlifts, as well as pilots and planes who fought in the Battle of Britain and the Blitz. During the Battle of Britain between 88 and 112 Canadian pilots served in the RAF, most had come to Britain on their own initiative. For political necessity an "all Canadian" squadron was formed under the British Commonwealth Air Training Plan at the start of the war and the Squadron served in the Battle of France. They were later joined by No. 1 Squadron RCAF in June 1940 during the Battle for Britain and they were in "the thick" of fighting in August, by the end of the battle in October 1940, 23 Canadian pilots had been killed. Squadrons of the RCAF and individual Canadian pilots flying with the British RAF fought with distinction in Spitfire and Hurricane fighters during the Battle of Britain. By 1 January 1943, there were enough RCAF bombers and crews in Britain to form No. 6 Group, one of eight bomber groups within RAF Bomber Command. If the planned German invasion of Britain had taken place in 1941, units of the formation later known as I Canadian Corps were already deployed between the English Channel and London to meet them.