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The Navaho and the X-10

11 May 2022

29º 19’ 50” N / 81º 45’ 57” W

Only a few months after the surrender of Japan, which finally ended World War II (WW II), North American Aviation (NAA) submitted a three step proposal for a paradigm setting weapon design rooted in Nazi Germany’s V-2 rocket design. A missile, but with a wing to enhance its range, to carry a nuclear weapon from the United States to Cold War opponents across continents. NAA was answering a request from the U.S. Air Force (USAF) requiring an interim weapon system to compliment manned strategic bombers until the intercontinental ballistic missile (ICBM) was developed and deployed.

Incredibly, though WW II aviation was dominated by a myriad of subsonic piston engine powered aircraft only a decade prior, NAA had designed a Mach 3 cruise missile powered by a pair of ramjets which was launched to altitude and speed with a twin engine rocket booster. It was called the SM-64 Navaho which vertically launched using Rocketdyne XLR83 (200,000 pound thrust each) rocket engines to 70,000 feet at a speed of Mach 3 and separate from the Navaho—whereupon the Navaho’s Wright Aeronautical XRJ-47 (15,000 lbs thrust each) ramjets could start and send the nearly 90 foot long cruise missile on a 5000 mile ride to deliver a nuclear warhead (the CEP goal back in the day was 2.3 miles).

That was the dream anyway.

The USAF had assigned a priority to the program second only to ICBM development. 

Production management may have been an issue but dreams and aspirations were well ahead of design and manufacturing. On the face of it, the $700 million (~$7.4 billion in 2022 dollars) was an abysmal failure. Well behind schedule and over budget, the Navaho’s first flight was not until the mid 1950s. Its longest flight was for a tad over 42 minutes. Overall, total Navaho flight time was merely 1-1/2 hours over 11 launches. Many flights crashed due to engine failure and the longest was 500 miles out of an intended 1500 mile route.

Total failure.

Or was it?

The Navaho program was a technology incubator. Mach 3 speeds required new titanium alloys for much better heat resistance (though the air is much less dense at 70,000+ feet the fuselage temperatures range up to 660º F). The unmanned 5000 mile range flight envisioned spurred better inertial auto navigation equipment and this system found its way to the A-5 (formerly the A3J) Vigilante, the USS Nautilus (SSN-571) on its record voyage under the Arctic ice to the North Pole and the AGM-28 Hound Dog cruise missile. Note that both the Vigilante and the Hound Dog were both North American Aviation products, as well.

SM-64 Navaho cruise missile with booster displayed at Cape Canaveral ages ago (Florida Memory image)

All the foregoing noted, the era of the cruise missile would have to wait a few more decades. Interestingly, there is a rare example of a Navaho with its booster and that is displayed on the Cape Canaveral Space Force Station (formerly Cape Canaveral AFB). Curiously, though, a booster sans engines is located at VFW Post 10208/AmVets Post 1208 in Salt Springs Florida.

North American SM-64 Navaho Booster Rocket at VFW Post 10208/AmVet Post 1208 in Salt Springs FL (note the pylon which would mate to the Navaho cruise missile)—Joseph May/Slipstream Photography ©2022
North American SM-64 Navaho Booster Rocket at VFW Post 10208/AmVet Post 1208 Salt Springs FL—Joseph May/Slipstream Photography ©2022

Closely related to the Navaho is the NAA X-10 which was the test vehicle for the Navaho concept. Resembling the SM-64 Navaho missile it was also unmanned but instead powered by two Westinghouse J40 turbojets which produced the X-10’s speed into the Mach 2 range. Additionally, for reusability, it differed from the Navaho in having landing gear for conventional taking off and landing (Navaho engineers were not concerned about landing). NAA gained insight flight testing the X-10 to higher Mach speeds as well as aerodynamic characteristics of the delta wing as well as the fully moving canard surfaces. These insights were also explored in future projects subsequent to the Navaho such as the NAA XB-70 Valkyrie. Like the SM-64, there is a rare example of an X-10 which survives and it is displayed in the National Museum of the U.S. Air Force.

North American Aviation’s X-10 at the National Museum of the U.S. Air Force (note the deflection limit lines of the fully-flying canard surfaces)—museum image
North American Aviation X-10 in flight—National Museum of the USAF image

Information for this post was derived primarily from The Evolution of the Cruise Missile which was written by Kenneth P. Werrell and published in 1985. It can be downloaded as a PDF from the Air University Library at Maxwell AFB website.

One Comment leave one →
  1. Gareth Cook permalink
    11 May 2022 15:05

    Very informative. Thanks.

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