The Sikorsky R-6 was designed to improve on the earlier R-4 and incorporated numerous changes yet retained a generally similar layout (which was also shared with the R-5, although this was a more radical departure from the original design). The fuselage of the R-6 was more streamlined and longer than that of its predecessor, but the basic rotor and transmission system was retained. A more powerful Franklin engine replaced the Warner engine of the R-4, enabling superior flight characteristics including faster speed. Production was undertaken by both Sikorsky as well as Nash-Kelvinator although this resulted in difficulties and as a result, lower numbers were eventually provided to the US Navy and USCG as well as the RAF and FAA, the three main users besides the US Army (as with the R-4, the name Hoverfly II was adopted in British service). The R-4 entered service just after World War II ended and as such did not see combat as it had been replaced by more capable types by the time the Korean War broke out in 1950.

First flight of the XR-6 took place on 15 October 13 and entered service two years later as the R-6A (renamed H-6A after 1948 and also given the company designation S-49). US Navy units were known as the HOS-1 whereas those in RAF service were designated Hoverfly II.