The R-5 differed from the R-4 by having an increased rotor diameter and a new, longer fuselage for two persons in tandem,[1] though it retained the R-4's tailwheel-type landing gear.

[3] The remaining twenty were built as the three-place R-5D, which had a widened cabin with a two-place rear bench seat and a small nosewheel added to the landing gear, and could be optionally fitted with a rescue hoist and an auxiliary external fuel tank.

[1] With room for three passengers plus pilot, the S-51 was initially intended to appeal to civilian as well as military operators, and was the first helicopter to be sold to a commercial user.

[citation needed] The U.S. Navy ordered four S-51s "off-the-shelf" from Sikorsky in late 1946 for use in the Antarctic and Operation Highjump, placing them into naval inventory as the HO3S-1.

[6] Carried aboard the seaplane tender USS Pine Island, 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.

[7] The Navy equipped several warship classes with HO3S-1 utility helos, including aircraft carriers, seaplane tenders, icebreakers, Des Moines-class cruisers, and Iowa-class battleships.

[citation needed] During its service life, the H-5/HO3S-1 was used for utility, rescue, and mercy missions throughout the world, including flights during Operation Highjump in the Antarctic.

While the extra power of the H-5 made it significantly more useful than its R-4 and R-6 cousins, the H-5/HO3S-1 suffered, like most early small tandem-seat single-rotor machines, from center of gravity problems.

However, in conditions of high ambient temperatures, which reduced lift due to the lowered air density, all weights were jettisoned.

[11] The H-5/HO3S-1 gained its greatest fame during the Korean War when it was called upon repeatedly to rescue United Nations pilots shot down behind enemy lines and to evacuate wounded personnel from frontline areas.

[13] In the United Kingdom, the first scheduled daily helicopter service started in June 1950 between Liverpool and Cardiff using S-51s operated by British European Airways (BEA).