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The Wasp Jr. R-985 was the third engine type designed by Pratt & Whitney Aircraft, following the Wasp R-1340 and Hornet R-1690, all of which were nine-cylinder engines. Virtually a Wasp of reduced dimensions, the Wasp Jr. followed closely the details of construction throughout. The Wasp Jr., originally rated at 224 kW (300 hp), was first type certificated in January 1930. Designed for light transports, trainers, sport aircraft, and helicopters, number of R-985 models were made, most at 298 kW (400 hp) or more power. The R-985 powered a wide variety and large number of military and commercial aircraft, making it one of the most successful reciprocating engines ever built in its power class. The Jacobs Aircraft Engine Company of Pottstown, Pennsylvania built this Pratt & Whitney-designed R-985-AN5. Jacobs converted it for vertical helicopter installation. It powered the Sikorsky XH-5, YH-5A/D/E, H-5A/D/F/G and Kellett YH-10 helicopters.