After training in Canada, Blakeslee arrived in England on May 15, 1941, where he was assigned to No. 401 Squadron RCAF. The squadron was assigned to the Biggin Hill Wing. Flying sweeps over France, Pilot Officer Blakeslee seems to have first seen combat on November 18, 1941, when he damaged a Bf 109 near Le Touquet; and he claimed his first kill on November 22, 1941, a Bf 109 destroyed, over Desvres, about 10 miles south of Marck; on the same mission, he damaged a further Bf 109 whilst returning to base. His next kills were not claimed until April 28, 1942, two Fw 190 probably destroyed. He proved to be not a particularly good shot, but was receptive to the principles involved in air fighting tactics, and was soon shown to be a gifted leader, in the air and on the ground.