Early evolution of nuclear-armed bombers


B-29 and B-36


1948 … Boeing B-50 strategic bomber

The evolution of nuclear-armed bombers began with the use of the Boeing B-29 Superfortress, an aircraft designed in World War II to carry conventional weapons. Crews flew this aircraft to drop the 13-kiloton Little Boy atomic bomb that destroyed Hiroshima on August 6, 1945, and the 23-kilotonyield Fat Man that shattered Nagasaki eight days later. The B-29 and a variant, the B-50, then served as the U.S. Air Force’s only nuclear-capable bombers, under the Strategic Air Command, well into the early 1950s. Despite improvements to the propeller engine aircraft and the refinement of operations such as aerial refueling, they were too slow to avoid jet interceptors and lacked the range to hit targets from bases in the continental United States.

The B-50’s development was approved in 1944, when the aircraft was known as the B-29D. Still in the midst of war, the Army Air Forces (AAF) wanted a significantly improved B-29 that could carry heavy loads of conventional weapons faster and farther. As World War II ended, the production of thousands of B-29s was canceled. The B-29D survived, but its purpose was changed. Redesignated as the B-50 in December 1945, the improved bomber was now earmarked for the atomic role. The decision was prompted by the uncertain fate of Convair B-36, the first long-range, heavy bomber produced as an atomic carrier. Of course, some of the B-29s that had been modified to carry the atomic bomb remained available, and surplus B-29s were being reconfigured for the atomic task. Just the same, the B-29s of war vintage were nearly obsolete. Hence, they would have to be replaced by a more efficient, atomic-capable bomber pending availability of the intercontinental B-36 or of another bomber truly suitable for the delivery of atomic weaponry.

While the short-range B-50 was immediately recognized as a stopgap measure, the magnitude of the aircraft’s development problems proved unexpected. The B-50’s first difficulties stemmed from its bomb bay which, like that of the B-29, was too small to house the new bomb and its required components. The fast development of special weapons created more complications, since the individual components of every single type of bomb had to be relocated within the bomb bay’s narrow confines.

In keeping with the usual vicissitudes accompanying the development of any new or improved aircraft, the B-50 soon exhibited engine malfunctions. Then, cracking of the metal skin on the trailing edge of the wings and flaps dictated extensive modifications. And while these problems were being resolved, new requirements were levied on the aircraft. In 1949, as the proposed RB-36 remained a long way off, and because of the older RB-29’s deficiencies in speed, range, and altitude, some B-50s had to be fitted for the reconnaissance role. To make matters worse, fuel tank overflows, leaking fuel check valves, failures of the engine turbo-chargers, generator defects, and the like continued to plague every B-50 version.

Meanwhile, contrary to plans, most B-50s came off the production lines without the receiver end of the new air-to-air refueling system being developed by Boeing. Additional, and successful, modifications therefore ensued. Nevertheless, the Strategic Air Command (SAC) had no illusions. The B-50, along with the B-36 (first delivered in June 1948), would be obsolete in 1951. That the B-50 did not start leaving the SAC inventory before 1953 was due to the production problems and many modifications of its replacement: the subsonic B-47.

It began as an outgrowth of the B-29, the B-50 can be traced back to July 1939, when Boeing Airplane Company introduced Model 334A, the B-29’s first direct ancestor. Specifically, however, the B-50 bomber stemmed from a B-29 conversion, initiated in 1944.

Requirements for the B-29 Superfortress, from which the B-29D (later known as the B-50) derived, were issued in February 1940, when the Army Air Corps asked the aircraft industry to submit designs for a “Hemisphere Defense Weapon.” Boeing Model 345 (a further development of Model 334A) was adjudged best of all proposals for bombers with very-long-range characteristics, and the company was authorized in September 1940 to produce the first very heavy bomber to incorporate pressure-cabin installations and other radical changes in design and armament. Development of an improved version of the famed B-29 began in 1944, as a so-called Phase II evolution of the basic design. No specific requirements ensued, but the main intent was to equip the improved bomber with the new Pratt & Whitney R-4360 Wasps and to do away with existing and often troublesome versions of the Curtiss-Wright R-3350 radial engines. The B-29A assigned to the Phase II development project, once reconfigured with the new Wasp engines, was flown by Boeing as the YB-44 prototype. The AAF approved within a few months a production version of the YB-44, which was then designated as the B-29D, and ordered 200 production models of the improved bomber in July 1945.

Japan’s surrender on 14 August 1945, 3 months after the defeat of Nazi Germany, prompted the cancellation of military procurement. In the process, the 200 B-29Ds on order since July 1945 were reduced to 60 in December of the same year.

The B-29D became the B-50 in December 1945. Officially, the aircraft’s new designation was justified by the changes separating the B-29D from its predecessors. However, according to Peter M. Bowers, a well-known authority on Boeing aircraft, “the redesignation was an outright military ruse to win appropriations for the procurement of an airplane that by its designation appeared to be merely a later version of an existing model that was being canceled wholesale, with many existing examples being put into dead storage.

In any case, the former B-29D featured many changes. The redesignated aircraft, built with a stronger but lighter grade of aluminum, had larger flaps, a higher vertical tail (that could be folded down to ease storage in standard size hangars), a hydraulic rudder boost, nose wheel steering, a more efficient undercarriage retracting mechanism, and a new electrical device to remove the ice from the pilot’s windows. The new aircraft’s wings and empennage also could be thermally de-iced. Finally, the 4 higher-thrust Pratt & Whitney R-4360 engines that replaced the standard B-29’s R-3350s gave a power increase of 59 percent, and electrically controlled, reversible-pitch propellers allowed the use of engine power as an aid to braking on short or wet runways. There was also some rearrangement of the crew. Yet, no matter what designation, there was no doubt that the piston-powered B-29D/B-50 would seem antiquated in the post-war era of jet bombers.

The AAF began to plan for an atomic strike force in the first few months of peace that followed the end of World War II. It ordered that 19 additional B-29s be reconfigured as atomic carriers in July 1946, six months after the improved B-29D had become the B-50. Most likely, the AAF already planned that the redesignated bombers would first supplement the reconfigured B-29s and then replace them until a better atomic carrier became available. But the AAF at the time was not in a particularly strong position to press for what it believed to be essential. Hence, the true purpose of the B-50 program did not become official until the spring of 1947.

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