When United Aircraft Corp.'s JT15D engine was first considered for potential high-altitude, low flight speed, long-endurance RPV applications by the U.S. Air Force, the questions were: 1.Will the engine run at these altitudes? 2.Can it deliver the required thrust? 3.Can it deliver the required power extraction? 4.What is the specific fuel consumption? 5.What oil system modifications are needed? 6.What is the optimum control system? 7.Are there other unknowns? A JT15D-4 turbofan engine, with only minor modifications which were easily incorporated into engines coming off the production line, proved more than adequate to achieve predicted endurance goals and measured performance.