At the outbreak of the Korean War in 1950, the USAF found itself in dire need of an all-weather interdiction aircraft. The piston-engined Douglas A-26 Invaders were limited to fair weather operations and were in short supply. On 16 September 1950, the USAF issued a request for a jet-powered bomber with a top speed of 630 mph (1,020 km/h), ceiling of 40,000 feet (12,190 m), and range of 1,150 miles (1,850 km). Full all-weather capability and secondary reconnaissance role had to be included in the design. To expedite the process, only projects based on existing aircraft were considered. The contenders included the Martin XB-51, and the North American B-45 Tornado and AJ Savage.
Unusually, the service considered foreign aircraft, including the Canadian Avro Canada CF-100 Canuck and the new British English Electric Canberra, which had not yet officially entered service with the Royal Air Force (RAF). The AJ and B-45 were quickly dismissed, because their outdated designs had limited growth potential. The CF-100, an all-weather interceptor, was too small and lacked sufficient range. The XB-51, while very promising and much faster, had limited maneuverability, a small weapons bay and limited range and endurance.
On 21 February 1951, a British Canberra B.2 flown by Roland Beamont became the first jet to make a nonstop unrefueled flight across the Atlantic Ocean, arriving in the United States for USAF evaluation. In a 26 February flyoff against the XB-51, the Canberra emerged a clear winner. It was officially taken up by the USAF on 25 May 1951.
However, because its production lines were working at full capacity to meet the Royal Air Force orders, English Electric was unable to produce additional aircraft quickly enough for USAF requirements, and on 3 April 1951, Martin was granted a license to build Canberras, designated B-57 (Martin Model 272) in the United States. To expedite production, the first B-57As were largely identical to the Canberra B.2, with the exception of more powerful Armstrong Siddeley Sapphire engines of 7,200 lbf (32 kN) of thrust instead of Rolls-Royce Avons, also license-built in the United States as Wright J65s. In addition, canopy and fuselage windows were slightly revised, the crew was reduced from three to two, wingtip fuel tanks were added, engine nacelles were modified with additional cooling scoops, and the conventional "clamshell" bomb bay doors were replaced with a low-drag rotating door originally designed for the XB-51.
The first production aircraft flew on 20 July 1953, and was accepted by the USAF a month later on 20 August. During the production run from 1953 to 1957, a total of 403 B-57s were built.