On 25 January 1951, Wernher von Braun presented to the Army his findings on the Hermes C1 '500-mile-missile' that he had been directed to develop. The use of available components could shorten the time required for the development of a prototype. Two liquid-propellant rocket engines already under development could meet von Braun's requirements.
North American Aviation had developed the XLR43-NA-1 for the booster for its long-range Project MX-770 cruise missile (later dubbed Navaho). It was essentially a redesigned and improved version of the V-2 rocket engine which von Braun's team was most familiar. Some former members of the Peenemuende rocket team had participated in its development.
The other rocket engine project found to merit serious consideration was the AJ 10-18 developed by Aerojet Engineering Corporation. This was expected to develop 712 kN thrust from four swivel-mounted thrust chambers. Von Braun's team found that the Aerojet proposal was late, Not Invented Here, still only in the proposal stage, and too powerful for the Hermes C1 - it would be more suited for use in a two-stage ballistic rocket.
The North American engine was expected to be ready for quantity production by the late summer of 1951. In response to a request for a detailed development program to modify this engine to Army needs, North American proposed the establishment of a "general technical program for the design, modification, and testing of a 333-kN thrust rocket of 110 seconds duration and with special thrust decay characteristics at cutoff . The Ordnance Corps let a cost-plus-fixed-fee, research and development, letter order contract on 27 March 1951. The $500,000 contract provided for 120 days of research and development efforts, required North American Aviation to modify the design and performance characteristics of the XLR43-NA-1 engine to meet the specifications of the Ordnance Corps. It also required the company to manufacture and deliver to the Ordnance Corps a mockup and two complete prototypes of the modified engine (designated the NAA 75-110).
The Ordnance Corps issued numerous supplemental agreements that enlarged the scope of work required of North American Aviation during the life of the contract. For example, where the contract originally required the contractor to deliver only two complete prototypes, a supplement on 26 April 1952 increased the quantity by an additional seventeen. A supplement on 20 January 1953 provided for the contractor to conduct a program of engineering and development to improve the design, reliability, servicing, handling characteristics, and performance of the rocket engine; and to provide analysis, design changes, fabrication of test hardware, and development tests. Other modifications of the contract directed North American Aviation to perform a reliability and endurance test program, to provide spare parts for the rocket engines, to fabricate and provide simulated test equipment (with spare parts) for the NAA 75-110 engines, and to modify the 17 rocket engines in accordance with the technical direction from the Guided Missile Development Division. The Ordnance Corps made no further increase in the number of rocket engines that were being purchased through this contract. . Rather, the remaining quantity required in both the research and development and the industrial programs were purchased by subcontract by the production missile prime contractor, Chrysler. The Army's direct contract with North American for the 17 engines totaled $9,414,813 when closed out in September 1960.
Because the development program for the NAA 75-110 engine and the flight tests of the research and development missiles were being conducted concurrently, the Guided Missile Development Division was in an excellent position to provide technical direction on the incorporation of modifications or improvements in the engine components. As a result, improvements in the performance features and components of the NAA 75- 110 engine yielded seven different engine types for use in the research and development missiles. Designated A-1 through A-7, each different type engine had the same basic operational procedures and was designed for the same performance characteristics as every other NAA 75-110 engine. Each type differed from the others only in modifications of various components. All seven engine types were interchangeable, as only minor tubing modifications were required for mating the engine to the missile. The differences were as follows:
Of the 19 engines, 12 were used in flight test vehicles. The remaining seven were used in shipping, and storage tests; test of inspection equipment; training of inspectors; and in static firing tests.
Thrust (sl): 367.400 kN (82,595 lbf). Thrust (sl): 37,468 kgf. Engine: 658 kg (1,450 lb). Thrust to Weight Ratio: 64.21.
AKA: NAA 75-110; NAA 75-110.
Status: Out of production.
Unfuelled mass: 658 kg (1,450 lb).
Diameter: 1.77 m (5.80 ft).
Thrust: 414.30 kN (93,138 lbf).
Specific impulse: 265 s.
Specific impulse sea level: 235 s.
Burn time: 155 s.
First Launch: 1950.
Number: 148 .