Part II : 1950 -1957
Switch from Air-Breathing to Rocket Engines
 Up to 1952, military concepts for long-range missiles emphasized rocket-boosted, winged missiles powered by air-breathing engines.* Beginning that year, a series of events brought great changes in military thinking about strategic missiles. These events, according to Herbert York, a participant, were "the invention and demonstration of the hydrogen bomb, the election of Eisenhower and the concomitant extensive personnel changes throughout the executive branch, . . . and the growing accumulation of intelligence reports ... that the Soviet Union had already launched a major program for the development of long-range rockets."20
In June 1952, the Department of Defense established a study group on guided missiles which led to the Strategic Missiles Evaluation Committee, chaired by John von Neumman, the famed mathematician.** The von Neumman committee studied the Air Force's strategic missile program and reported in February 1954 that both the missile systems and their specifications were out of date and unsatisfactory. An urgent need for greater strategic missile capability was seen because of improved Soviet defenses against manned bombers as well as rapid development of Soviet strategic missiles. The committee pointed out that progress in weaponry research allowed reduction of warhead mass as well as a relaxation of accuracy requirements.21 The von Neumman committee recommendations had great influence and when adopted and implemented, long-range missile development swung from winged missiles using airbreathing engines to ballistic rockets-the beginning of the accelerated ballistic missile development of the 1950s. In the first series of liquid-propellant missiles, the propellants were a kerosene-like hydrocarbon and liquid oxygen.
The choice of a single propellant combination for development of long and intermediate range liquid-propellant ballistic missiles did not stop research on high-energy propellants, which became candidates for a second generation of improved missiles.
The NACA was not oblivious to the changes in military emphasis from air-breathing to rocket engines, but took no strong, steps to realign its research emphasis until about 1956. Meanwhile, the small rocket group at the Lewis laboratory was steady on its course and late in 1954 was ready, at long last, to experiment with liquid hydrogen.