Begun in 1947, the B-54 was the planned production version of the YB-50C prototype. The standard Pratt & Whitney R-4360 engines of the normal B-50 bomber were replaced with R-4360-51 Variable Discharge Turbine (VDT) engines, the fuselage was lengthened by over 10 feet (3.0 m) and the wingspan was extended by 20 feet (6.1 m), which required the installation of outrigger landing gear in the numbers one and four engine nacelles. Large fuel tanks under the outboard wing section were required to carry an additional 3,000 US gallons (11,000 l; 2,500 imp gal) of fuel to reach the intended 9,300 miles (15,000 km) range; 14 .50-caliber machine guns comprised the specified defensive armament.
On May 29 1948, contracts were placed by the Air Force for 21 B-54A bombers and 52 RB-54A reconnaissance aircraft;[N 1] However, on April 18, 1949, the B-54 project was cancelled due to the development of better-performing jet aircraft; construction of the prototype B-54A had started at Seattle but was never completed. The cancellation was lambasted by the Seattle press, who claimed that it was a political decision instead of a military one.
^While the numbers given in the article are based on the official US Air Force serial number assignments, sources vary on how many were ordered. Seven B-54As and 23 RB-54As is one number given;; other sources specify 14 B-54As and 29 RB-54As. Several sources state the total order was 43 aircraft, while one claims 73.