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The Challenger engine, which followed the water cooled Curtiss V-8 OX-5 engine that powered the World War I JN-4 “Jenny” trainer aircraft, was designed as a lower-cost, medium-power engine specifically intended for small commercial cabin aircraft and open cockpit sport planes. The engine received its original Approved Type Certificate (No. 5) in 1928, which was revised and re-issued in 1930. The small, compact configuration of two staggered rows of three cylinders was intended to provide better dynamic balance and, thus, smoother operation, as well as low frontal area for improved airframe streamlining and better pilot visibility. However, although being economical, the Challenger did not run smoothly, and was frequently replaced by aircraft owners because of a vibration problem. The Challenger powered a variety of aircraft types including the Curtiss Robin, Curtiss Fledgling, Curtiss Tanager, Curtiss-Wright Sedan 15-C, Command-Aire Model 5C3, and Eastman Sea Rover E-2.