This XH-39 set a new world helicopter speed record of 251 km/h (156 mph) on 26 August 1954. It was preserved at Fort Rucker in 1957. The S-59 was a heavily modified S-52 with a Continental XT51 turboshaft, developed from the French Turbomeca Artouste, and retractable landing gear.

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.

The S-59 or XH-34 (originally YH-18B) was a development from the S-52-2 (YH-18A) with an XT51 (Artouste) turbine engine, four-blade rotor and retractable landing gear. Two XH-39s modified from H-18s. Seen in Building 6008 at Fort Rucker, this is the XH-39A, former c/n 52007, which flew and broke a few world records; the other XH-39, 49-2891 (c/n 59002) reportedly never flew as such. Type rejected in favour of Bell H-40 Huey. One civilian S-59, N74150, was also built and is preserved in the New England Air Museum. Photo by: Alan Wilson