Williams F121 on display at the National Museum of the United States Air Force
Type Turbofan
Manufacturer Williams International
First run 1984
Major applications AGM-136 Tacit Rainbow

The Williams F121 (company designation WR36-1[1]) is a small turbofan engine designed for use in the AGM-136 Tacit Rainbow anti-radiation cruise missile.

Development and design

The F121 engine had a rare set of design parameters as it is designed to be used only once. As a cruise missile engine, it was designed to have a long shelf life (be able to sit around unused for long periods of time) and then operate when needed for several hours.[2] It was designed to power the AGM-136 Tacit Rainbow, which was to be a stand-off anti radiation missile. Its first flight was on July 30, 1984. The AGM-136 program was canceled several years later.

Another unique feature of the engine is that it was started with an explosive cartridge because it couldn't start while still mated to its aircraft.[2]

In the late 2000s, the engine was being used by the Naval Air Warfare Center at Naval Air Weapons Station China Lake to test fuel performance and additives.[3]


Data from [2][3]

General characteristics



See also

Related lists


  1. ^ Leyes, p. 421
  2. ^ a b c Williams International F-121 Fanjet. National Museum of the US Air Force Fact Sheet. Accessed 17 July 2017.
  3. ^ a b Kraemer, Nathan A. (2007). Development and Qualification of a Specialized Gas Turbine Test Stand to Research the Potential Benefits of Nanocatalyst Fuel Additives. Master's Thesis, Naval Postgraduate School.