Part II : 1950 -1957
 The National Advisory Committee for Aeronautics (NACA), established in 1915 to develop practical solutions for the problems of flight, showed interest in liquid hydrogen as a fuel in 1939 but did nothing about it for over a decade. The early interest came as a surprise to Robert Goddard when he visited NACA's director, George W. Lewis, in March 1939. He learned that "the NACA is considering liquid H [hydrogen] as a fuel (!) possibly used with air for rocket propulsion."1 Four days after his visit, still amazed, Goddard wrote to a friend:
On talking with Dr. Lewis of the NACA I found that they are contemplating using liquid hydrogen, because of its low weight and high heat value, as a fuel with atmospheric air. I mention this because liquid hydrogen is expensive and difficult to transport and store ... and also because tanks of it have to be surrounded by liquid oxygen or liquid nitrogen. It makes my use and advocation of liquid oxygen seem really conservative by comparison. The main point is that even with the extreme difficulty of liquid hydrogen, its use is being considered by a body as serious as the NACA.2
What did Lewis have in mind? The use of atmospheric air rather than readily available liquid oxygen suggests that he may not have been thinking of a simple rocket for propulsion but a rocket as a component in an air-breathing engine, possibly applied to a turbine engine. He may have heard about the early work of Hans von Ohain, employed in April 1936 by Ernst Heinkel to develop a turbojet engine. Pressed for time, von Ohain turned to gaseous hydrogen as a fuel for convenience in tests beginning in early 1937 and found that his turbojet engine worked well using hydrogen.*
 On the other hand, Lewis had long been thinking about rocket research, for 18 months earlier he had asked NACA member Charles A. Lindbergh, then in England, "for recommendations with reference to any rocket research for the National Advisory Committee for Aeronautics to carry on."3 Lindbergh, in turn, sought the advice of Robert Goddard who suggested "several lines of research: for example, liquid propulsion rockets for gliders; application of rockets to turbines; rockets for accelerating and decelerating planes; development of combustion chambers of large thrust."4 In 1938 Lewis wrote to Goddard expressing interest in his high-speed work and Goddard asked for NACA wind-tunnel tests to determine the flight stability of his rockets. Was Lewis thinking of Goddard's suggestion of applying rockets to turbines, a concept appearing later as a "turborocket"? Whatever Lewis had in mind remains a mystery for, characteristically, he kept his planning informal and shared it with few others. The incident, however, illustrates the dual nature of NACA during that period- receptive to new ideas but conservative and slow in entering new fields of research. It also indicates the ease with which liquid hydrogen comes to mind when engineers think of high-energy fuels.
In 1944, seven years after asking Lindbergh about recommendations for rocket research and apparently after some prodding by Wright Field, Lewis authorized the construction of four simple rocket test cells at the Aircraft Engine Research Laboratory in Cleveland.5
The information on German jet propulsion and rocket developments, which increased from a trickle in 1943-1944 to a flood of captured documents in 1945, made NACA officials realize how far behind they had fallen in these new propulsion systems. In the fall of 1945, a sweeping reorganization of the Cleveland engine laboratory caught all but senior officials by surprise. Overnight, research emphasis shifted from piston engines to jet engines (turbojet and ramjet) with some work on rockets. The rocket research was kept small because of the conservative nature of NACA and the influence of its chairman, Jerome C. Hunsaker, who shared with many the belief that rockets were more applicable to artillery than aircraft and had no place in an aeronautical research laboratory. The word "rocket" was avoided in the organizational name in favor of "high-pressure combustion."
The rocket group at the Cleveland laboratory concentrated on high-energy, liquid-propellant rocket engines with teams working on propellant performance (theoretical and experimental), combustion, and cooling.** The propellant work followed the logical path of computing the theoretical performance of several fuel-oxidizer combinations over a range of operating conditions and selecting the most promising for experimental investigation. By 1948, Riley Miller and Paul Ordin reported calculations of a number of propellant combinations containing hydrogen, nitrogen, and oxygen atoms, with liquid hydrogen giving the highest exhaust velocity and having the lowest propellant density.6 The same year, Vearl Huff and his associates made a major contribution to theoretical performance techniques by developing a convergent, successive approximation method that saved considerable time over other methods.7
 High-energy rocket propellants were difficult to obtain, for most were available only in small quantities. The NACA researchers passed by liquid hydrogen in favor of hydrazine and diborane as fuels and 100 percent hydrogen peroxide, chlorine trifluoride, liquid oxygen, and liquid fluorine as oxidizers.8
Calculated risks were taken to transport comparatively rare samples to the laboratory. Louis Gibbons, chief of fuels research, brought a gallon of pure hydrogen peroxide from Buffalo clamped between his knees in an all-night train ride. Paul Ordin used much the same method in bringing a sample of hydrazine from St. Louis. The first diborane, nested in dry ice, was delivered by private automobile from Buffalo. The first liquid fluorine was obtained from downtown Cleveland and transported in a special laboratory-built trailer escorted by police.9
During the 1947-1949 period, diborane was of great interest as a rocket fuel, but experiments soon revealed that it had great disadvantages and its theoretical promise could not be realized. When used with liquid oxygen or hydrogen peroxide, diborane formed boron oxides which deposited in the rocket nozzle and degraded performance.10 When used with liquid fluorine, the combustion products were volatile, but the absence of deposits was replaced with a greater problern-difficulty in cooling. The theoretical flame temperature of diborane-fluorine under rocket operating conditions is about 5400 K, far higher than many other propellants. Moreover, neither diborane nor fluorine is suitable as a regenerative coolant, which means a third fluid is required for cooling, seriously degrading performance. Although experimental performance of diborane-fluorine was measured, it became apparent by the early 1950s that diborane was not a good rocket fuel.11 The experience with diborane showed not only the limitations of theoretical considerations in selecting propellants but also the value of experiments in revealing practical problems.
In 1949, the acceleration in aeronautical research brought another major reorganization to the Lewis Flight Propulsion Laboratory.*** Its director remained Edward R. Sharp, a gregarious and able administrator who had started as an apprentice at the Langley laboratory. Technical management was strengthened by elevating Abe Silverstein to chief of research.
The reorganization brought a pleasant surprise to the small rocket group. It was moved up one level in the organizational hierarchy, named for what it was, and given more personnel. Silverstein was the highest NACA official to show significant interest in rocket research, although much of it was new to him. One of the things he wanted to understand better was the propellant selection process and, particularly, how candidates for research were chosen.
During the same period, organizational changes were occurring in related military research and development. In 1949, a USAF advisory committee headed by Louis N. Ridenour recommended that the Air Force research and development activities be consolidated into a single command. In January 1950, the Air Force established the Air Research and Development Command which included the facilities at Wright Field and the Air Engineering Development Center at Tullahoma, Tennessee-the latter renamed in honor of General Arnold the following month.
 The reassessment of research plans that followed the organizational changes had special significance for the Lewis rocket group in March 1950 when a group of Wright Field officials visited the Lewis laboratory.**** The visitors showed considerable interest in rocket research in general and propellant selection in particular. Also discussed were the merits of forming a NACA subcommittee on rockets, a need recognized by the Durand committee nearly a decade earlier.