The development of the XB-45 was initiated in August 1944 in response to a spring 1944 request by the Army Air Force for proposals using the newly developed General Electric J35 axial-flow turbojet engine. The AAF issued requirements for a 500 mph top speed, a 1,000-mile combat radius and service ceiling of at least 40,000 feet. North American submitted its preliminary design studies in December and got approval for full-scale development in March 1945. Besides the North American XB-45, the Consolidated XB-46, Boeing XB-47 and Martin XB-48 resulted from the Army request.
The XB-45 was powered by four J35s arranged in pairs in wing-mounted nacelles. The Army considered jet bombers to be so fast that only the tail of the aircraft needed to be defended. The XB-45 carried only two .50-cal. machine guns in the tail. The power-assisted turret guns were fired manually by a tail gunner. The rest of the four man crew consisted of a pilot, copilot-radio operator and bombardier-navigator. The normal bomb load of the XB-45 was 8,000 lbs., but it was capable of carrying one 22,000 lb. "Grand Slam" bomb.
Three XB-45 prototypes were built and the first flight was March 17, 1947. The XB-45 competed against the four-engine XB-46 and proved superior. An initial production contract for 97 aircraft, built as B-45A, made the aircraft the first production all-jet bomber to enter service with the USAF.
TECHNICAL NOTES: Armament: Two .50-cal. machine guns in the tail and 8,000 lbs. of bombs; note the aircraft could carry one 12,000-lb. "Tall Boy" or one 22,000-lb. "Grand Slam" bomb Engines: Four Allison J35-A-11 turbojets of 4,000 lbs. thrust each Maximum speed: 500 mph Cruising speed: 419 mph Range: 2,920 miles Service ceiling: 38,500 ft. Span: 89 ft. 6 in. Length: 74 ft. 0 in. Height: 25 ft. 2 in. Weight: 66,820 lbs. (gross weight) Crew: Four (pilot, copilot-radio operator, bombardier-navigator, tail gunner) Serial numbers: 45-59479 to 45-59481