The helicopter HUP-1 has been developed by the Piasecki company 1948. Parallel with the serial production the new modification HUP-2 was developed with more powerful engine R-975-42 and autopilot. The US NAVY has purchased 165 helicopters HUP-2, another 15 machines were transferred to French NAVY. The helicopters were used to transport cargo and passengers, and also performed the rescuing functions. In 1951 the NAVY has placed an order with Piasecki for new modification of the helicopter with the reinforced cabin flooring. The land modification has been designated H-25A 'Army Mule'. The US Army has purchased 70 of such helicopters.