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 T-64 powered Caribou on 22 September 1961).
An Egyptian Air Force DHC-5D
De Havilland's design, the DHC-5 Buffalo, was chosen as the winner of the United States Army competition in early 1963, with four DHC-5s, designated YAC-2 (later CV-7A and subsequently C-8A) ordered. The first of these aircraft made its maiden flight on on 9 April 1964. All four aircraft were delivered in 1965, the Buffalo carrying nearly twice the payload as the Caribou while having better STOL performance. No further US orders followed, however, as at the start of 1967, inter-service politics lead to large fixed-wing transports being transferred to the United States Air Force, who considered themselves adequately equipped with the Fairchild Aircraft C-123 Provider.
Company data claims a takeoff distance over a 50 ft (15 m) obstacle of 1,210 ft (369 m) at 41,000 lb (18,597 kg) and a landing distance of over a 50 ft (15 m) obstacle of 980 ft (299 m) at 39,100 lb (17,735 kg) for the DHC-5A model.