The B-45 officially originated back in August 1944, at a time when the USAAF was already aware of German advances in the field of jet propulsion, especially as applied to the development of jet bombers. Alarmed by German developments, the War Department called for bids from the aviation industry on a new family of jet-powered bombers, with gross weights ranging from 80,000 pounds to more than 200,000 pounds. Requirements for a top speed of 500 mph, a 1000-mile combat radius, and service ceiling of at least 40,000 feet were also issued. These new aircraft were to be powered either by TG-180 or TG-190 engines which were then under development at General Electric. The TG-180 was eventually built by the Allison Division of General Motors as the J35, and the TG-190 was built by the General Electric company as the J47.
In 1944, North American Aviation of Inglewood, California submitted a design known under the company designation NA-130 as its proposal in response to the War Department request. The NA-130 was a shoulder-wing monoplane of fairly conventional layout with a dihedral tailplane and a retractable landing gear. The Model 130 was to be powered by four turbojets, grouped in horizontal pairs, one pair under the wings on each side of the fuselage outboard of the tailplane.
A Letter Contract dated September 8, 1944 called for the development of three experimental aircraft based on the NA-130. The designation XB-45 was assigned. At the same time, three other contractors were also awarded development contracts, Convair for the XB-46, Boeing for the XB-47, and Martin for the XB-48.
The end of the Second World War resulted in the cancellation of many projects and the delay of others. However, the War Department felt that the development of a jet-powered bomber should still be pressed forward with the utmost speed, and the XB-45, XB-46, XB-47, and XB-48 contracts were left untouched. In 1946, rising tensions with its erstwile Soviet ally caused the USAAF to assign a high priority to the development of a jet-powered bomber. In response to this new sense of urgency, the USAAF decided to forego the competition that would ordinarily be held between the four entries and opted instead to review the available designs to see which of the contestants could be produced first.
By mid-1946, the XB-45 and XB-46 were nearing completion, but the XB-47 and XB-48 were still at least two more years away. Since the USAAF was guided by what it felt to be a sense of great urgency, it decided to appraise the XB-45 and XB-46 right away and choose one of them for immediate production. Any consideration of the XB-47 and XB-48 would be deferred until after they had flown. if either the XB-47 or XB-48 turned out to be markedly superior to the plane that was then being produced, then that aircraft would be purchased and the currently-produced version would be phased out. This is indeed what happened when the XB-47 appeared.
The USAAF concluded that the Convair XB-46 would likely be inferior in performance to the XB-45, and that its thin, graceful fuselage would not be able to hold all the required radar equipment. Since the configuration of the XB-45 did not depart significantly from that of proven aircraft already in service and hence presented fewer risks, on August 2, 1946, the USAAF announced that they were going to endorse the immediate production of the B-45. A contract for 96 B-45As (North American N-147) was signed on January 20, 1947, even before the XB-45 had made its first flight.
The XB-45 was a shoulder-winged monoplane powered by four Allison-built General Electric J35-A-4 turbojets paired side-by-side in large nacelles underneath each wing. The tailplane had a large dihedral angle in order to clear the jet exhaust. The crew consisted of two pilots sitting in tandem underneath a transparent canopy, a bombardier in a transparent nose, and a gunner sitting in the extreme tail. It was assumed that jet bombers would be so fast that only the tail of the aircraft needed to be defended. The three forward crew members entered the aircraft by means of a large door on the left hand side of the nose, with the tail gunner having his own door in the right fuselage underneath the tailplane. The main landing gear was mounted just inboard of the engine nacelles, and retracted inward into wells in the wing roots.
The first XB-45 took off on its maiden flight on March 17, 1947 from Muroc Army Air Field, piloted by George Krebs. The aircraft did not have a greenhouse bombardier's compartment, but a fake greenhouse was painted on the nose. On that first flight, the aircraft had to be flown under severe speed restrictions, since the landing gear doors would not close properly. It was the first American four-jet bomber to fly.
Three XB-45s were built. Each of the three XB-45s was instrumented for a different specialized phase of the program. Near the beginning of the test flight program, one of the XB-45s crashed, killing two of North American's test pilots. A total of 131 flights were carried out by the surviving two aircraft before they were turned over to the USAF.
The USAF accepted one of the surviving XB-45s on July 30, 1948, the other on August 31. Initially, they did not have cabin pressurization, but this was later added. In June of 1949, one of the XB-45s was damaged beyond repair in an accident. The remaining XB-45 had only a limited testing value due to an initial shortage in government-furnished equipment. A USAF flight test crew delivered the plane to the Wright- Patterson AFB in Ohio, where equipment was installed for bombing tests at Muroc AFB in California, but very few tests were actually carried out because of excessive maintenance requirements. On May 15, 1950 the aircraft was transferred to the Air Training Command to serve as a ground trainer.
Engines: Four Allison J35-A-7 turbojets, rated at 4000 lb.s.t. each. Performance: Maximum speed 483 mph at 30,000 feet, 516 mph at 14,000 feet, 494 mph at sea level. Service ceiling 37,600 fet. Initial climb rate 2070 feet per minute. An altitude of 30,000 feet could be attained in 19 minutes. 2236 miles range with 8350 pounds of bombs, 1700 miles range with 14,000 pounds of bombs. Maximum range 2921 miles. Weights: 41,876 pounds, 66,820 pounds gross, 82,600 pounds maximum. Dimensions: Wingspan 89 feet 6 inches, length 74 feet 0 inches, height 25 feet 2 inches, wing area 1175 square feet.