Part II : 1950 -1957
First Attempt to Use Liquid Hydrogen
 When the rocket subcommittee met in October 1954, preparations for the first experiment with liquid hydrogen were almost complete. The liquefier was producing liquid hydrogen. One of the larger test cells had been equipped to use liquid hydrogen with either of two oxidizers-liquid oxygen or liquid fluorine. Edward Rothenberg headed the team using hydrogen-oxygen and was ready first.* On 23 November 1954, the first successful run with liquid hydrogen was made; thrust and chamber pressure were at design values and exhaust velocity was 90 percent of theoretical. Ten days later, two more successful runs were made, but performance data were incomplete. A fourth successful run on 6 January 1955 yielded lower performance than the previous runs.22
After the four successful runs with liquid hydrogen-oxygen in 22-kilonewton engines, no more experiments with liquid hydrogen were undertaken for almost a year. The reasons were several. One was a need to reassess injector design. On the first three runs the oxidizer injection rings had burned, and the low performance of the fourth was a clear signal of poor injection. Another reason was a need for improved start and shutdown techniques. Although a satisfactory method had been worked out, it depended a good deal on the reaction time and skill of the operator. In starting, a low hydrogen flow was ignited outside the engine and flashed back into the engine when oxygen flow began. When flashback occurred, full hydrogen and oxygen flows were established. After the first run, the operators discovered that a fire had started during the ignition phase, which ignited hydrogen escaping from the supply tank. The problem was solved by opening the hydrogen valve and burning the escaping hydrogen until the tank was exhausted. The experience was somewhat similar to the leaks encountered by Walter Thiel in Germany about 1937 (p.269).
Two other factors contributed to the delay in hydrogen testing. The Air Force loaned the laboratory the mobile hydrogen liquefaction equipment developed by Herrick L. Johnston (fig.14) which would produce almost twice as much liquid hydrogen as the installed equipment and help keep pace with growing demands for hydrogen in other laboratory work. Glenn Hennings of the rocket staff was placed in charge of getting the mobile equipment into operation. The other factor was increasing interest in the possibility of upgrading the performance of existing missiles using JP fuel-oxygen by adding a small quantity of fluorine to the oxygen.** The fluorine not only increased performance but made the combination self-igniting. By 1955, three reports had been written on investigations of JP4 fuel with mixtures of oxygen and fluorine.23 This concept was not tried in a missile, however, because of concern over the toxicity of fluorine.
 The rocket subcommittee was still concerned over the low level of NACA rocket Research when it met in November 1955.*** resolution was passed detailing the importance of rocket research, the concern over the low level of NACA activity, and the problems needing attention; it ended by recommending the NACA effort "be considerably increased so that significant progress can be made at the pace keyed to the swiftly moving national defense effort in rocket propulsion."24 Development of the Atlas and Titan ICBMs and Thor and Jupiter IRBMs was accelerating and subcommittee members from propulsion and airframe manufacturers as well as the military were feeling the pressure. They believed that the NACA ought to help solve their development problems.
NACA officials recognized the increased emphasis on missiles but continued research on advanced air-breathing engines as well. In the 1955 NACA annual report, Chairman Hunsaker stated: "Today, problems associated with a nuclear engine for aircraft propulsion and with an intercontinental ballistic missile are perhaps the most pressing." 25 The nuclear engine for aircraft was soon to fade into oblivion, but the intercontinental as well as the intermediate-range ballistic missiles became key elements in U.S. military preparedness.
** JP (jet propulsion) fuel was the designation for the petroleum blend similar to kerosene, used at the time. Later rockets used RP (rocket propulsion) fuel.
*** Thomas E. Myers
of North American Aviation replaced Maurice Zucrow as chairman in
1954, with Zucrow continuing as a member. Other members: Lt. Col.
Langdon F. Ayers, USAF-ARDC; R.B. Canright, Douglas Aircraft; B.F.
Coffman, Bu. Aer., Navy; H.F. Dunholter, General Dynamics; R.B.
Foster, Bell Aircraft; W.P. Munger, Reactoin Motors; J.R. Patton,
Office of Naval Research; C.C. Ross, Aerojet-General; C.N.
Satterfield, M.I.T., F.E. Schulltz, General Electric; A.J.
Stosick, JPL; R.C. Swann, Redstone Arsenal; F.I. Tanczos, Bu.
Aer., Navy; the author, NACA-Lewis and b.E. Gammon, secretary.