The Buffalo arose from a 1962 United States Army requirement for a STOL transport capable of carrying the same payload as the CH-47A Chinook helicopter. De Havilland Canada based its design to meet the requirement on an enlarged version of its DHC-4 Caribou, already in large-scale service with the United States Army, to be powered by General Electric T64 turboprops rather than the Pratt & Whitney R-2000 piston engines of the Caribou. (It had already flown a T64-powered Caribou on 22 September 1961).