B-1

Development
The B-1 was conceived as the Advanced Manned Strategic Aircraft (AMSA) program around 1965. AMSA was the last in a series of 1960s programs that looked at replacing the B-52 with a long-range multi-role supersonic aircraft that could drop bombs and launch nuclear missiles.[2]


[edit] The Valkyrie and changing tactics
In December 1957, U.S. Air Force selected North American Aviation's proposal to replace the B-52 Stratofortress. This would lead to the B-70 Valkyrie.[3] The Valkyrie was a six-engine bomber that could fly very high at Mach 3 to avoid interceptor aircraft, the only effective anti-bomber weapon in the 1950s. At the time, Soviet interceptors were unable to intercept the high-flying Lockheed U-2;[4] the Valkyrie was to fly at similar altitudes and much higher speeds. But by the late 1950s, anti-aircraft surface-to-air missiles (SAMs) could threaten high-altitude aircraft,[5] as demonstrated by the downing of Gary Powers' U-2 in 1960.

Recognizing this, the USAF Strategic Air Command had begun moving to low-level penetration before the U-2 downing. This greatly reduces radar detection distances while at that time SAMs were ineffective and interceptors less effective against low-flying aircraft.[6] Also the flight path to a target could be routed around known anti-aircraft sites, and the landscape could be used to the bomber's advantage to stay out of the radar's line-of-sight operation. Aircraft speed became much less important. The targets themselves often had defenses located nearby to prevent this sort of approach all the way in, but stand-off weapons such as the AGM-69 SRAM provided an attack capability from outside the defensive missile's range. Low-altitude flight also made the bombers very difficult to detect from aircraft at higher altitudes, including interceptors, as radar systems of that generation could not "look down" due to the clutter that resulted from ground reflections.

Operations at low levels would limit the B-70 to subsonic speed, while dramatically decreasing its range due to much higher fuel requirements. The result would be an aircraft with similar speed but much less range than the B-52 it would have replaced. The Mach 2 B-58 was similarly limited to subsonic speeds at low altitudes. Unsuited for this new role, the viability of the B-70 as a bomber was questioned. Citing high cost, a growing ICBM force, and poor survivability against missiles,[7] the operational bomber fleet was canceled in 1961 by President John F. Kennedy, and the program was changed to a supersonic research program with two XB-70 prototype aircraft.[8]


[edit] B-52 soldiers onAlthough never intended for the low-level role, the B-52's flexibility allowed it to outlast its intended successor as the nature of the air war environment changed. The B-52's large airframe and ample internal room made it relatively simple to add greatly improved electronic countermeasures suites. Additionally, no other aircraft had anything close to the B-52's bombload capacity when used in the tactical role. With improved coordination with ground spotters, B-52s with "big belly" modifications delivered up to 60,000 pounds (27,215 kg)[9] of high explosive bombs during the Vietnam War. The same would not have been true of the Valkyrie, which featured a much smaller bombload of 25,000 pounds (11,000 kg).[10]

That was not to say the B-52 was a perfect aircraft. Higher speed would aid even a low-level approach in the strategic role, something the F-111 was taking advantage of. In the high-load tactical role the B-52 was limited to a small number of airfields due to its very long takeoff roll. By the early 1960s the state of the art in engine and airframe design had improved considerably; an aircraft designed to match the B-52 in performance could meet both of these additional requirements as well. Although the B-52 had proven to be surprisingly adaptable in both the strategic and tactical roles, during the early 1960s a number of studies followed these technical developments in order to design a worthy B-52 replacement.