1955 the US Air Force issued System Requirement No.
22 for Weapon System (WS) 110A, a chemically powered
bomber to succeed the B-52 in SAC service from
1963. This aircraft was to be able to deliver
thermonuclear weapons to targets within the Soviet
Union from bases in the continental US. The
weapons were to be free-fall bombs or a 300+
nautical mile range cruise missile. The bomber
itself was to have an un-refuelled radius of more
than 4000 nautical miles, with a subsonic cruise and
high supersonic dash over the target.
Both Boeing and North American Aviation studied
various designs to meet this requirement. The
winning North American proposal was ultimately
developed into the XB-70 Valkyrie, which flew in
prototype form in 1964. The Boeing
configurations ranged from 16-engined developments
of the B-52 to trapezoidal and delta winged
A more radical concept developed by Boeing but used
by both competitors was the "floating panel".
In this arrangement, the outer wings of the
aircraft, with their own fuel pods, undercarriage
and even engines, acted as sub-craft and were free
to rotate in flight to eliminate loads on the
central airframe. After the subsonic cruise
section of the flight, these outer panels would be
jettisoned and the bomber would accelerate to
supersonic speeds for the attack. Although the
use of large jettisonable pods had been demonstrated
on the Convair B-58 Hustler, the idea was not
carried forward and the final designs presented by
North American and Boeing were monolithic bombers.