Concurrent with the Snark, another cruise missile had its brief moment in the sun. Compared to the Snark, the North American Navaho was much more dramatic and ambitious. Although the two air-breathing intercontinental missiles developed together, USAF planned to get the subsonic Snark into operations first, followed by the supersonic Navaho. Eventually, both would move aside for ballistic missiles.
In December 1945, the Technical Research Laboratory of North American Aviation submitted a proposal to the Air Force to continue German missile research, apparently in response to military requirements issued late that year. North American proposed a three stage effort: first add wings to a V-2, then substitute a turbojet-ramjet powerplant for the German rocket engine, and finally couple this missile with a booster rocket for intercontinental range. In April 1946, the Air Force bought the first part of this scheme under project MX-770, a 175- to 500 mile range surface-to-surface missile. In July 1947, it added the 1,500-mile range, supersonic ramjet to the program. By March 1948, the program called for a 1,000-mile test vehicle, a 3,000-mile test vehicle, and a 5,000-mile operational missile. In 1950, the Air Force considered launching a Navaho from a B-36, an idea dropped the next year. Finally, in September, USAF firmed up the program, that is, not further changing it. The Navaho program called first for the design, construction, and test of a turbojet test vehicle, followed by a 3,600-mile-range interim missiles and culminating in a 5,500-mile-range operational weapon.
USAF designated the first step, the turbojet test vehicle, the X-10. Two Westinghouse J40WE-1 turbojets powered the X-10, which first flew in October 1953. The missile was 70 feet long, configured with a canard, "V" tail, and 28-foot delta wing. Radio controls and landing gear permitted recovery. In all, 11 vehicles flew 27 flights. On the 19th test, the North American missile reached a maximum speed of Mach 2.05, establishing a speed record for turbojet-powered aircraft.
Unfortunately, problems hindered the follow-on (interim) missile, the XSM-64, and schedules slipped badly. In March 1952, USAF estimated that the first acceptance would occur in January 1954; it occurred in April 1956, 27 months late. Similarly, a January 1954 estimate expected the first flight in September 1954, a flight actually not attempted until November 1956. The first successful flight did not come until well into 1957. There was no single problem; difficulties seem to affect just about everything except the airframe. The most serious problems, however, centered on the ramjets and auxiliary power unit, the latter not operating successfully until February 1956.
Between the summers of 1954 and 1955, USAF considered pushing the XSM-64 into operational service, but problems and delays in the basic program killed that idea. The Air Force did accelerate the Navaho program in late 1955, giving it a priority second only to that of the ICBMs (intercontinental ballistic missiles) and IRBMs (Intermediate Range Ballistic Missiles), aiming to get the intercontinental- range missile operational by October 1960.
The XSM-64 resembled the X-10 in size and configuration. The big difference was a 76-foot, 3-inch long booster that was used piggy-back fashion with the XSM- 64. Together, the two measured 82 feet 5 inches in length and were launched vertically.
As impressive as the XSM-64 looked on paper and to the eye, in reality the system proved far different. The XSM-64 flight tests disappointed all, earning the project the uncomplimentary appellation, "Never go, Navaho." The first XSM-64 launch attempted in November 1956 ended in failure after a mere 26 seconds of flight. Ten unsuccessful launch attempts occurred before a second Navaho got airborne on 22 March 1957, for four minutes and 39 seconds. A 25 April attempt ended in an explosion seconds after liftoff, while a fourth flight on 26 June 1957 lasted a mere four minutes and 29 seconds.
Little wonder then, with the lack of positive results, cost pressures, schedules slippages, and increasing competition from ballistic missiles, that USAF canceled the program a few weeks later in early July 1957. The Air Force did authorize up to five more XSM-64 flights at a cost not to exceed $5 million. These tests, "Fly Five," occurred between 12 August 1957 and 25 February 1958. Although harassed by problems and failures, the vehicle exceeded Mach 3, with the longest flight lasting 42 minutes and 24 seconds. The final Navaho tests consisted of two launches in project RISE (Research in Supersonic Environment), which were equally unsuccessful. On the first flight on 11 September 1958, the ramjets did not start and on the second and last flight on 18 November 1958, the missile broke up at 77,000 feet. It cost the taxpayers over $700 million to gain less than 1 hours of flight time. So ended the Navaho project.
Nevertheless, USAF saw the Navaho project as a leap forward in the state of the art of missile technology. The Navaho required new technology that resulted in a complex missile. For example, aerodynamic heating (300 at Mach 2 and 660 at Mach 3) demanded new materials. North American used titanium alloys, much stronger than aluminum and yet 40 percent lighter than steel, as well as precious and rare metals at contact points on much of the electrical gear. Other untested technology and areas of risk included the canard configuration, ramjets, guidance, and the massive rocket booster. The situation required North American to develop and then manufacture these various pieces of new technology concurrently.
On the positive side, although the Navaho did not get into service, some of its components did. Some went into other equally unsuccessful North American projects such as the F-108 and B-70. Others fared better. The Redstone used the rocket engine concept, and the Thor and the Atlas adapted the engine. The Hound Dog, the nuclear submarine Nautilus for its epic under-the-ice passage of the North Pole, and the Navy's A3J-1 Vigilante bomber, all adapted the Navaho's inertial autonavigation system. Therefore, while the Navaho proved costly, the program did have positive benefits.