In 1953 the US Army awarded a contract to Sikorsky for the experimental conversion of 3 H-18 (S-52) helicopters from piston to turbine power. Of the three aircraft, two were designated XH-39s by the Army (49-2890 was used for testing and 49-2891 was a static test frame that never flew). The XH-39 was in competition with the Bell XH-40. The Army chose the XH-40, which became the UH-1 Huey. This is the third H-18 converted, designated S-59 by Sikorsky, and was used by the company demonstration and publicity flights, for example static display at the World's Fair in New York in 1964.