Early Air Force Interest in Large Engines and Vehicles
 The development of the Atlas intercontinental ballistic missile had hardly begun to accelerate when the Air Force research and development arm began considering larger rocket engines for larger vehicles. In 1955, the Air Force contracted with the Rocketdyne division of North American Aviation to. study the feasibility of a single-chamber engine with a thrust of 1.3 to 1.8 meganewtons (300 000-400 000 lb). Rocketdyne designated this engine the E-1 and the same year announced that a singlechamber engine of 4.5 meganewtons (1 million lb of thrust) was also feasible.1 There were no specific requirements for these large engines, but presumably the Air Force was looking ahead to the need to carry larger ballistic payloads and perhaps to manned spaceflight or boost-glide hypersonic aircraft concepts such as Dynasoar.
At the November 1956 meeting of the fuels and propulsion panel of the USAF Scientific Advisory Board (p.189), large rocket engines were considered. The panel recommended that the Air Force study the feasibility of very large rocket engines on the order of 22.3 meganewtons (5 million lb of thrust). This was far larger than any that had been considered; the minutes do not reveal the panel's reasons for such interest.  The Air Force waited over a year before replying to this recommendation. The reply mentioned the work begun at Rocketdyne in 1955 and indicated that future Air Force requirements for thrusts greater than 4.5 meganewtons could probably be met more efficiently by clustering "appropriately-sized" smaller engines. A vehicle requirement for 22.3 meganewtons could be met in the same manner. The Air Force reply left unclear what size engines it was interested in, but the same month Wright Field initiated a design competition for a single-chamber engine of 4.5 meganewtons. The proposals were evaluated and a contract awarded to Rocketdyne in June 1958. The large engine was designated the F-1.2