 Complete the following phrase:  CAM sailings were initially limited to North American convoys with aircraft maintece performed by the Royal Canadian Air Force at Dartmouth, Nova Scotia. CAM ships sailed on Gibraltar and Freetown convoys beginning in September 1941, after an aircraft maintece unit was established at the RAF base at North Front, Gibraltar. No CAM aircraft were provided during January and February 1942 after it proved impossible to maintain the catapult-mounted aircraft in flying order during the North Atlantic winter. CAM sailings resumed on 6 March 1942 on North Atlantic convoys and in April on the 