By 1964 the Soviets already possessed small nuclear warheads capable of extending the kill ratio of the SA-2 to 19,680 ft and the ceiling to 80,000 ft.
The Valkyrie program suffered numerous delays due to inexperience with the new heat-resistant materials, as well as political and budgetary reasons. When the prototype XB-70 AV-1 was flown on September 21, 1964 the Soviet air defense system was already so consolidated that the WS110A specification was meaningless and the B-70 was cancelled by the Kennedy Administration.
In August 1958, the North American project office submitted the proposal Defensive Antimissile System (DAMS) using air-to-air missiles launched by the Valkyrie.
The Defense Feasibility Study was completed in March 1959 and published by the Air Proving Ground Center-Eglin AFB the same month the U-2 incident occurred.
In 1948 the first experimental AAM-A-2 air-to-air missile was launched and entered in service with the USAF in 1955 as the Hughes AIM-4 Falcon.
The original purpose of the Falcon was a Mach 3.8 self-defense weapon for the B-52 bomber and was shortly revived during the B-70 development. The rail-launched missile was not a particularly maneuverable and needed to be pointed in the right direction of the target.
Due to the B-70 speed the Falcon could just be used against any threat coming from its forward hemisphere, but the Valkyrie would have to defend itself against threats from all direction with spherical coverage.
The Falcon was a cylindrical rocket with four delta wings. Would it have been thrown sideways from a B-70 flying to Mach 3 it would have been destroyed by the crosswind shock waves.
North American proposed the Weapons System WS-740A, a wingless lenticular-form rocket with omnidirectional launch capabilities, capable of engaging incoming missiles at relative speeds of Mach 10 and being able to survive and maneuver at 250g accelerations.
The project was awarded to the Convair Division of General Dynamics Corporation, under the codename Pye Wacket, in June 1959.
