After Nazi Germany's progress in the ground of jet force in 1943, The US Army Air Forces asked the General Electric Company to invent a more influential engine than its axial turboprop. Result was the innovation of the J35 and J47 turbojets. In 1944, after requirement of jet engine were establish, the War Department asked the manufacturer to submit proposals for jet bombers. 

The requirements included that the gross weight of the aircraft should range from 80000 to 200000 pounds. Only four contractors responded to the call. As there were time constraints, the Army Air Force dropped the regular procedures like common supplier competition and appraisal of the designs.

The B-45, proposed by the North American Aviation, Inglewood, California, had a multi jet engine which was bigger and more conventional than the Boeing XB-47; giving it an edge over the competitor. Like all bombers produced after the end of World War 11, the B-45 was designed to carry both conventional and atomic bombs. After the Army Air Force tested the bomber, it suggested some pre-production changes. The manufacturer then increased the aircraft's stabilizer area, redesigned the nose panel and increased the tail-plane by nearly 7 feet. In August 1948, 22 B-45s reached the Army Air Force who however felt that the increased weight, unnecessary takeoff distance and some mechanical defects halted the aircraft’s bright future.  

All control surfaces of the B-45 were hydraulically boosted, and an electrically actuate tab on the elevator maintained longitudinal trim. The aerodynamic power of the trim-tab-elevator combination was something, the pilots desired for years. During ‘inadvertent maximum tab deflection’, the pilot's strength even became insufficient to overcome the large elevator hinge moments if the hydraulic boost system failed or was turned off. However, the technology of power-assisted controls was in its early years at that time, and much was yet to be learned about the effective and safe application of such control techniques.

In a B-45, two pilots seated in tandem under a transparent canopy, a bombardier located in the nose, and a tail gunner. Altogether, there were sits for four crews though only the pilots were equipped with ejection seats. In an emergency, the bombardier could evacuate through a hatch located in the side of the fuselage. To minimize the hazards associated with the high-velocity airstreams, a fuselage flap was installed near the hatch to deflect the airstreams away from the exiting bombardier. There was an escape hatch with deflector flaps for the tail gunner. Environmental control of the aircraft included pressurization, heating, and cooling.

The aircraft had a gross weight of 110, 050 pounds; similar to Boeing B-29; but in speed, B-45 was faster by 200 miles per hour. B-45 could deliver a 10 000-pound weapon load at a mission radius of 1008 miles and Ferry range was around 2426 miles. The maximum lift-drag ratio of the B-45 was 16.3, about the same as that of the B-29, but the zero-lift drag coefficient was a much lower 0.0160 as compared with 0.0241 of B-29. Pilots of B-45 however found that speed and flight-path angle during the landing maneuver, difficult to control. For its low thrust range, changes in thrust with throttle movement needed a longer time which made the rendered control of the flight difficult. On the other hand, at higher thrust levels, changes in thrust with time were speedier. These problems worked as lessons during designing later jet-powered bomber aircrafts.

B-45 made its initial flight on March 17, 1947. It was the first jet-powered bomber, produced in the US; as well as the first aircraft to be incorporated in the newly formed USAF. The North American Aviation later developed more capable B-45C model that differed largely from the initial B-45. For instance, it had 1200-gallon fuel tank mounted at each wingtip. At the same time, the Boeing announced production plans of B-47, which worked as a potential threat for future production of B-45s. In mid 1948, USAF authority questioned B-45's intrinsic value. After that, when President Truman's budgetary axe slashed Air Force expenditures, B-45’s production was reduced to 142.

Despite this setback, the B-45 regained importance soon after. In mid 1950, the US military took a decision to work on the big bombers so that they can carry large quantities of small atomic and thermonuclear weapons in the Korean peninsula and in the European Theater. This decision led to the ‘Backbreaker’ program, involving complex modifications of the existing aircrafts; so that they can carry atomic bombs and large amounts of new electronics support equipments. B-45 was part of this program. Some 40 B-45s also had to be equipped with a new defensive system and extra fuel tanks.

The Atomic capable 40, B-45s began reaching the United Kingdom in May 1952. These aircrafts were than equipped with jet engines instead of propellers driven by reciprocating power plants. The wing of B-45 had airfoil thickness ratio of 14 % and was equipped with ‘trailing-edge’ single-slotted flaps. Side control of the aircraft was accomplished with the use of conventional ailerons. Due to the low drag, only a small amount of engine thrust was required in the approach configuration.

The B-45 served efficiently as an investigative aircraft in the Korea. It later performed classified, deep penetration photographic intelligence missions over many cold war communist countries. The ‘reconnaissance’ version of the B-45 became the predecessor of the U-2 and SR-71 surveillance aircrafts.

Final retirement of B-45 took place in 1958 ant the entire contingent, Backbreaker and reconnaissance models slowly phased out by 1959.

Overall, the B-45 program included 3 experimental XB-45s aircraft; one of which was completed as a preproduction example. 96 of them were B-45As while 10 B-45Cs and 33 RB-45Cs.