During the First World War over 20,000 Canadians volunteered to serve with the Royal Flying Corps (RFC) and the Royal Naval Air Service, producing such aces as William Barker, W.A. "Billy" Bishop, Naval Pilot Raymond Collishaw, Roy Brown, Donald MacLaren, Frederick McCall, and Wilfrid "Wop" May. In 1917 the RFC opened training airfields in Canada to recruit and train Canadian airmen. The Canadian government advanced the RFC money to open an aircraft factory in Toronto, Canadian Aeroplanes, but did not otherwise take part.