The S-61R differs significantly in a number of ways from the original S-61, in that it has a more capacious boat-type hull, modified to take a rear loading ramp, while the two sponsons have been replaced by two stub wings set farther back, into which the rear members of the tricycle landing gear retract.

The prototype was built by the company as a private venture and flown with a civil registration on 17 June 1963. However, the USAF had already placed an order with Sikorsky in February of that year for 22 aircraft, designated CH-3C, and they began to receive the first helicopters at the end of 1963. Subsequent orders brought the total number for the USAF to 133.

The CH-3C was used in the Vietnam War for rescuing pilots who had been shot down and came to be nicknamed the "Jolly Green Giant"; it was given more powerful turbines from February 1965 and redesignated CH-3E. The uprated "Green Giant" could carry 26 troops or 15 wounded, or vehicles of equivalent weight, and could also be armed with two Emerson turrets on the leading edges of the two stub wings. Forty-two CH-3Es were built, in addition to which 41 CH-3Cs were modified to this standard. The USAF also asked for specific modifications to be made to this helicopter to meet the demands of the Vietnam War: application of armour; use of supplementary fuel tanks for extended flights; self-sealing internal fuel tanks and a telescopic in-flight refuelling probe. Two of the first aircraft of the 50 to be built in the HH-3E rescue version became famous in 1967 by flying non-stop from New York to Paris (for the Air Show), covering the 6870km journey with nine refuellings by airtankers.

In August 1965, the US Coast Guard ordered a special version of the HH-3 which was given the designation HH-3F Pelican. This paramilitary American rescue service needed an aircraft with all-weather capability, which could safely land on water, and the HH-3F was the ideal solution. The Pelican was virtually identical to the HH-3E, apart from the lack of protection, armament and other military equipment. It had an AN/APN-195 search radar on the port side of the nose. The US Coast Guard received 40 HH-3Fs. The only foreign license-holder for this variant was Agusta, who began producing it in 1974. The 22 aircraft built by Agusta were all delivered to the Italian Air Force as replacements for the old, amphibious Grumman Albatross used for search and rescue missions at sea.

G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984

Technical data for Sikorsky CH-3C

Engine: 2 x General Electric T58-GE-1 turboshaft, rated at 969kW, main rotor diameter: 18.90m, fuselage length: 17.45m, height: 5.51m, take-off weight: 9750kg, max speed: 261km/h, cruising speed: 232km/h, hovering ceiling, OGE: 2600m, range with max fuel: 748km, payload: 3630kg