The Piasecki PD-18 (US Navy designation HUPRetriever, US Army designation H-25A Army Mule) was an American single-engined tandem-rotored helicopter of the 1950's developed for the US navy for a multi-use helicopter. A version was also produced for the US army with minor modifications. The Piasecki PD-18 was powered by a Continental R-975-46 engine providing a top speed of 170 kmh and a range of 630 km. The Piasecki PD-18 carried a crew of two and up to four passengers or three stretcher cases. Research Piasecki PD-18