The H-5 was originally built by Sikorsky as its model
S-48, designated as the R-5 by the United States Army Air Forces. It was designed to provide a helicopter having greater useful load, endurance, speed, and
service ceiling than the
Sikorsky R-4. The R-5 differed from the R-4 by having an increased rotor diameter and a new, longer fuselage for two persons in tandem, The first XR-5 of four ordered made its initial flight on 18 August 1943. In March 1944, the Army Air Forces ordered 26
YR-5As for service testing, and in February 1945, the first YR-5A was delivered. This order was followed by a production contract for 100 R-5s, outfitted with racks for two
litters (stretchers), but only 34 were actually delivered. Eleven S-51s were ordered by the USAF and designated the
R-5F, while 92 went to the Navy as the
HO3S-1, commonly referred to as the 'Horse'. Carried aboard the seaplane tender , on Christmas Day 1946 an HO3S-1 of VX-3 piloted by Lieutenant Commander Walter M. Sessums became the first helicopter to fly in the Antarctic. Having proved its capabilities, the initial naval HO3S-1 order was followed by subsequent purchases of an additional 42 aircraft in 1948. The Navy equipped several warship classes with HO3S-1 utility helos, including
aircraft carriers, seaplane tenders,
icebreakers, s, and s. By February 1948, the Marine Corps had equipped HMX-1, its first regular Marine Helicopter Transport Squadron, with six HO3S-1 aircraft. With a passenger load of only three lightly dressed persons, the HO3S-1s were primarily operated in the utility role by the marines; for the transport role, an additional nine tandem-rotor Piasecki-built
HRP-1 helicopters were later added to the squadron. Eventually, the U.S. Navy would acquire a total of 88 HO3S-1 (S-51) helicopters. Thirty-nine additional specialized rescue helicopters were built, as the
H-5G, in 1948, while 16 were fitted with
pontoons as the
H-5H amphibian in 1949. The R-5 had been designated under the United States Army Air Forces system, a series starting with R-1 and proceeding up to about R-16. In 1947 with the start of the United States Air Force, there was a new system, and many aircraft, but not all, were redesignated. The R-5 became the H-5. The United States Army broke off with its own designation system in the 1950s, resulting in new designations for its helicopter projects. In 1962 under the new tri-service system (see
1962 United States Tri-Service aircraft designation system), many navy and army aircraft were given the low numbers. Under the 1962 system, the low H numbers were given to new aircraft. For example, H-5 was given to the
OH-5, a prototype design which never entered Army service. ==Operational history==