Part II : 1950-1957
Air Force Evaluation of Rex I
 In June 1954, Col. Omar E. Knox sent the WADC evaluation of Rae's proposal to ARDC Headquarters. Three laboratories, including the power plant laboratory, contributed to the evaluation. The basic engine was considered technically feasible, but considerable doubt existed regarding the technical feasibility of the propeller, hydrogen system, and airframe. If the airplane could be built as predicted, it would be...
....extraordinary in performance. Rae was praised as an imaginative and competent engineer, as evidenced by his contributions while working for the Applied Physics Laboratory and by the analysis he submitted. At the same time, however, the evaluators questioned the wisdom of placing development of an airplane with a company with so little systems capability. The cost estimate was considered unrealistic. Knox recommended against accepting the proposal, but suggested that ARDC look into overall propulsion and airframe problems of aerodynamically supported aircraft at extreme altitudes. That was exactly what Heaton and Ayers had been doing and why they were interested in Rae's proposal. They were not satisfied with WADC's negative response.21
In July 1954, Col. Paul Nay replaced Heaton as chief of the ARDC division of aeronautics and propulsion and was soon involved in concepts for achieving high altitude flight, including Rae's. On 9 August, Rae and Wood visited Nay and Ayers at ARDC headquarters in Baltimore and the following day Rae sent his proposal to Nay.  It contained details on program phasing and cost. Rae estimated first year costs at $1.9 million and annual costs for the next three years at $3.1 million. Included was a $50 000 sum to contract with Lockheed Aircraft Company for an airframe analysis. Rae stressed that hydrogen was more a working fluid than a fuel and that its complete oxidation was not desirable. He had done additional analysis, and the application for the long-range, high-altitude airplane included a reconnaissance radar picket as well as a bomber. Rae did not attempt to downgrade the potential problems and indeed mentioned several. He also pointed out that hydrogen could be used as a fuel in regular turbojet engines and that engine cycles using hydrogen had common elements that justified immediate component development. He requested the Air Force to provide a supply of liquid hydrogen in the Los Angeles area for component testing. To emphasize his point on the versatility of hydrogen, he sent the Air Force a report describing an engine cycle which later became known as Rex III.22 It used air as the oxidizer and will be described later.
Rae's visit to ARDC and the revised proposal strengthened the belief of Nay and Ayers that Rae's concept should be further investigated. Three weeks after the visit, on 31 August 1954, Nay directed WADC to prepare a development plan for high-altitude engines, including the Rex I engine. He emphasized the need for long-range, high-altitude aircraft and argued that the optimum speed had not been established. This was a crucial point, for most of the emphasis was on aircraft capable of supersonic speeds, whereas the propeller-equipped Rex I was subsonic. Nay pointed out that WADC emphasis was on fans and compressors for jet engines rather than propellers, and the latter needed attention along with the hydrogen-oxygen reheat turbine cycles conceived by Rae. WADC should-as appropriate-conduct studies, experiments, and preliminary development of promising high-altitude propulsion systems, including RexI. Summers Gyroscope was regarded as capable of analytical and experimental work with their existing facilities. WADC was encouraged to develop a working arrangement with an engine manufacturer and take maximum advantage of existing hydrogen technology, including rocket experiments. The directive was accompanied by a transfer of funds to accomplish it.23
The directive was clearly much broader in scope than merely contracting with Summers for the use of Rae's idea. The directive addressed the general problem of high-altitude propulsion, of which Rae's engine was one possible solution. While Summers was endorsed as capable of analytical and experimental work with their existing facilities, ARDC also suggested a working arrangement with an engine manufacturer. This constituted a limited endorsement and was not an arbitrary decision. Procurement experts had investigated Summers Gyroscope as a contractor, and the top procurement official of ARDC visited the company to satisfy himself about its capabilities for limited work on the concept.24