engines. A dual-engine version of this, XLR-71-NA-1 (240K), was used in the G-26 Navaho. With improved cooling, a more powerful kerosene-burning version was developed for the triple-engine XLR-83-NA-1 (405K), used in the G-38 Navaho. With all the elements of a modern engine (except a bell-shaped nozzle), this led to designs for the Atlas, Thor and Titan engines. Operational history The first launch attempt, on 6 November 1956, failed after 26 seconds of flight. Ten failed launches followed, before another got off successfully, on 22 March 1957, for 4 minutes, 39 seconds of flight. A 25 April attempt exploded seconds after liftoff, while a 26 June flight lasted only 4 minutes, 29 seconds. Officially, the program was canceled on 13 July 1957, after the first four launches ended in failure. In reality the program was obsolete by mid-1957 as the first Atlas ICBM began flight tests in June and the Jupiter and Thor IRBMs were showing great promise. These ballistic missiles however would not have been possible without the liquid fuel rocket engine developments accomplished in the Navaho program. The launch of the Soviet Satellite Sputnik in October 1957 only finished Navaho as the Air Force shifted its research money into ICBMs. But the technologies developed for the Navaho were reused in 1957 for the development of the AGM-28 Hound Dog, a nuclear cruise missile which entered in production in 1959. The Soviet Union had been working on parallel projects, The Myasishchev RSS-40 "Buran" and Lavochkin "Burya" and a little later, the Tupolev Tu-123. The first two types were also large rocket-boosted ramjets, while the third was a turbojet-powered machine. With the cancellation of the Navaho and the promise of ICBMs in the strategic missile role, the first two were canceled as well, though the Lavochkin project, which had some successful test flights, was carried on for research and development purposes, and the Tupolev was reworked as a big, fast reconnaissance drone. Operators : The United States Air Force canceled the program before accepting the Navaho into service. Survivors One remaining X-10 is on display at the United States Air Force Museum Annex at Wright-Patterson AFB, OH. A Navaho booster rocket, though not marked as such, is currently displayed in front of a VFW post in Fort McCoy, Florida. The other remaining Navaho missile was previously displayed outside the south entrance gate of Cape Canaveral Air Force Station, Florida. This survivor