The RTV-A-2 Hiroc (high-altitude rocket) was a product of the United States' first effort to develop an intercontinental ballistic missile (ICBM). The project was named MX-774. The project was canceled in 1947, but leftover funds were used to build and launch three of the planned 10 research vehicles designated RTV-A-2. The design included several innovations; the gimbaled thrust chambers provided guidance control, the internal gas pressure was used to support the airframe and the nose cap was separable. All of these concepts were later used on the Atlas missile and the first two on the Viking rocket. Also developed as part of MX-774 was the Azusa guidance system which was not used on the Hiroc missile but did contribute to the Atlas missile as well as many other early guided missiles launched from Cape Canveral. Design The Hiroc missiles were long, had a fin span (the maximum width of the rocket, accounting for the fins) of , a diameter of , an empty weight including payload of and a gross liftoff weight (GLOW) of . The missile's propulsion system consisted of an XLR35-RM-1 composed of four thrust chambers, built by Reaction Motors, which produced of thrust each and could independently swivel up to ten degrees on one axis. The gimbaling motion was used to control the flight path of the missile, replacing the system of the V-2 missile that used moving fins placed within a fixed engine. The gimbal system adds complexity to the engine mounting but preserves more of the energy of the rocket exhaust during maneuvering. The engine had a specific impulse of sea level. The Hiroc missile used liquid oxygen as its oxidizer, and alcohol for its fuel. The Hiroc missile did not have separate tanks for its fuel and oxidizer, which were instead contained in one tank separated by two bulkheads. The airframe of the rocket was supported by nitrogen gas pressure inside the tank, which could contain propellant or nitrogen gas when stored. Having gas pressure provide rigidity to the structure reduced the empty weight by requiring less metallic components for structural reinforcement, but made the missile fragile because it required continuous pressurization. The RTV-A-2 Hiroc had an airframe to propellant ratio three times better than the V-2. The nose cone, which contained instrumentation, would separate from the rocket booster. This made the rocket lighter as only the nose cone and its instruments and recording