12/31/2011. Remarks by Johan Visschedijk: "Based on the successful development and flight trials of the R-4 training helicopter, the USAAF wrote in 1942 a requirement for a rather larger type capable of performing a useful military job as an observation machine. The Vought-Sikorsky Model VS-327 which was designed to this specification followed closely the general layout of the R-4, with main and tail rotors shaft-driven from an engine in the fuselage, but it was a completely new design in detail.

The helicopter section of the company became Sikorsky Aircraft Division of United Aircraft Corporation when it was separated from Vought on January 1, 1943. The design received the new company designation S-48, four prototypes were ordered early in 1943 with the USAAF designation XR-5 (s/n 43-28236 to 43-28239) and a fifth was ordered later (s/n 43-47954). The first XR-5 flew on August 18, 1943, at Bridgeport, Connecticut, USA. It was powered by a 450 hp Pratt & Whitney R-985-AN-5 engine, and the crew of two was seated in tandem. Two of the five prototypes were later fitted with British equipment and designated XR-5A.

For service trials, the USAAF ordered 26 YR-5As (s/n 43-46600 to 43-46625), similar to the prototypes, and 100 R-5As, of which only the first 34 were built (s/n 43-46626 to 43-46659). Two of the YR-5s, s/n 43-46613 and 43-46618, were assigned to the USN in 1946, redesignated HO2S-1 they received the BuNo 75689 and 75690 respectively. The R-5As had provision for litter carriers on each side of the fuselage, and were the first helicopters to go into use with the Air Rescue Service.

Twenty-one R-5As (43-46606 and 43-46640 to 43-46659) became R-5Ds when modified to carry a second passenger and fitted with a 600 hp Pratt & Whitney Wasp Junior engine, rescue hoist, auxiliary external fuel tank, and a nose wheel. The five YR-5Es (43-46611 to 43-46615) were YR-5As modified to have dual control.

From the R-5 design, Sikorsky evolved the S-51 commercial helicopter (first flown on February 16, 1946), with a 49 ft (14.94 m) rotor, four seats in the cabin, nose wheel in place of tail wheel and increased gross weight. The USAF procured eleven aircraft of this type in 1947, designated R-5F. In June 1948, USAF helicopters were re-categorized with "H" (Helicopter) in place of "R" (Rotorcraft) designations, resulting in YH-5A, H-5A, H-5D, YH-5E and H-5F designations appearing for the Sikorsky types.

To supplement the H-5As used by the Air Rescue Service and to expand this work, 39 more helicopters were purchased in 1948. Designated H-5G (s/n 48-524 to 48-562), they were similar to the H-5F with rescue hoist and other equipment for their specialized role. The 16 H-5Hs (s/n 49-1996 to 49-2011) purchased in 1949 had a combination wheel/pontoon landing gear and further increased gross weight. In service until the mid-1960s, the H-5 was used in a variety of roles of which rescue was the most prominent."