to prove the general aerodynamics, guidance, and control technologies for vehicles two and three. The X-10 was essentially an unmanned high performance jet, powered by two afterburning Westinghouse J40 turbojets and equipped with retractable landing gear for take off and landing. It was capable of speeds up to Mach 2 and could fly almost . Its success at Edwards AFB and then at Cape Canaveral set the stage for the development of the second vehicle: XSSM-A-4, Navaho II, or G-26. Step two, the G-26, was a nearly full-size Navaho nuclear vehicle. Launched vertically by a liquid-fuel rocket booster, the G-26 would rocket upward until it had reached a speed of approximately Mach 3 and an altitude of . At this point the booster would be expended and the vehicle's ramjets ignited to power the vehicle to its target. The G-26 made a total of 10 launches from Launch Complex 9 (LC-9) at Cape Canaveral Air Force Station (CCAFS) between 1956 and 1957. Launch Complex 10 (LC-10) was also assigned to the Navaho program, but no G-26s were ever launched from it (it was only used for ground tests of the planned portable launcher). The final operational version, the G-38 or XSM-64A, was the same basic design as the G-26 only larger. It incorporated numerous new technologies, Titanium components, gimballed rocket engines, a Kerosene/LOX propellant combination, and full solid-state electronic controls. None were ever flown, the program being cancelled before the first unit was completed. The advanced rocket booster technology went on to be used in other missiles including the Atlas intercontinental ballistic missile and the inertial guidance system was later used as the guidance system on the first U.S. nuclear-powered submarines. Development of the first-stage rocket engine for the Navaho began with two refurbished V-2 engines in 1947. That same year, the phase II engine was designed, the XLR-41-NA-1, a simplified version of the V-2 engine made from American parts. The phase III engine, XLR-43-NA-1 (also called 75K), adopted a cylindrical combustion chamber with the experimental German impinging-stream injector plate. Engineers at North American solved the combustion stability problem, which had prevented it being used in the V-2, and the engine was successfully tested at full power in 1951. The Phase IV engine, XLR-43-NA-3 (120K), replaced the poorly-cooled heavy German engine wall with a brazed tubular ("spaghetti") construction, which was becoming the new standard method for regenerative cooling in American