The USAF Air Research and Development Command's (ARDC) requirement for WS-110A asked for a chemical-fuel bomber with Mach 0.9 cruising speed and "maximum possible" speed during a entrance and exit from the target. The requirement also called for a payload and a combat radius of . The Air Force formed similar requirements for a WS-110L intercontinental reconnaissance system in 1955, but this was later canceled in 1958 due to better options. In July 1955, six contractors were selected to bid on WS-110A studies. Boeing and North American Aviation submitted proposals, and on 8 November 1955 were awarded contracts for Phase 1 development.