The F135 originated with Lockheed Corporation Skunk Works, with efforts to develop a stealthy STOVL strike fighter for the U.S. Marine Corps under a 1986 DARPA program. Lockheed employee Paul Bevilaqua developed and patented a concept aircraft and propulsion system, and then turned to Pratt & Whitney (P&W) to build a demonstrator engine. The ground test demonstrator used the first stage fan from a F119 engine for the lift fan. The engine fan and core from the F100-220 were used for the core of the demonstrator engine, and the larger low-pressure turbine from the F100-229 was used for the low-pressure turbine of the demonstrator engine. The larger turbine was used to provide the additional power required to operate the lift fan. Finally, a variable thrust deflecting nozzle was added to complete the "F100-229-"Plus"" demonstrator engine. This engine proved the lift-fan concept and led to the development of the current F135 engine.