[1] The Sea King has its origins in efforts by the United States Navy to counter the growing threat of Soviet submarines during the 1950s.

The Sea King was initially designated HSS-2, which was intended to imply a level of commonality to the earlier HSS-1; it was subsequently redesignated as the SH-3A during the early 1960s.

Introduced to service in 1961, it was operated by the United States Navy as a key ASW and utility asset for several decades prior to being replaced by the non-amphibious Sikorsky SH-60 Seahawk in the 1990s.

The Sea King also performed various other roles and missions such as search-and-rescue, transport, anti-shipping, medevac, plane guard, and airborne early warning operations.

The Sea King has also proved to be popular on the export market with foreign military customers, and has also been sold to civil operators as well.

The S-61R was another important variant, which was the CH-3C/E Sea King, used by the U.S. Coast Guard as the HH-3F Pelican, and the Air Force's HH-3E Jolly Green Giant; this version had a ramp at the rear among other changes.

[2] During the late 1950s, the US Navy took advantage of recent aerospace advances, such as the turboshaft engine, by commissioning the development of a new large naval helicopter.

The specification included a dipping sonar, mission endurance of four hours, and the ability to support a weapons load of 380 kg (840 lb).

[4][5][6] The designation HSS-2 was applied, allegedly to imply a level of commonality to the earlier HSS-1, should political sentiment turn against the development of an entirely new rotorcraft.

These trials, which involved testing the folding mechanism of the main rotor blades and a series of takeoffs performed during winds of up to 50 mph (80 km/h), were completed successfully in mid-1961.

[7][8] Shortly after the completion of suitability trials, the US Navy formally accepted delivery of the first HSS-2 rotorcraft, which was subsequently re-designated as the SH-3A, in September 1961.

[12] The base design of the Sea King had proved sound and several aspects were judged to be potentially useful for other operators, thus Sikorsky elected to pursue the further development of the rotorcraft for other markets beyond the US Navy.

[13][14] Another noteworthy Sea King variant, the significant change this time being the adoption of a conventional fuselage, the Sikorsky S-61R, was also concurrently developed for transport and search and rescue (SAR) duties, this type being extensively operated by the U.S. Air Force and the U.S. Coast Guard.

It was also common for Sea Kings to be converted for non-ASW activities, these roles included minesweeping, combat search and rescue, and as a cargo/passenger utility transport.

[4] The aircrew on ASW-tasked Sea Kings were routinely trained to carry out these secondary roles as aircraft could often be quickly adapted to perform different missions in the face of operational needs.

[5] In normal operations, the Sea King typically would have a four-man crew on board; these being a pilot and copilot in the cockpit, and two aircrew stationed within the main cabin area.

[5] The adoption of an amphibious hull allowed a Sea King to conduct a water landing and, being completely watertight, would enable the rotorcraft to remaining floating for prolonged periods on the ocean's surface.

[32] Some later Sea King models featured the TACNAV digital navigation system (first generation GPS) and overhauled cockpit instrumentation for night vision compatibility.

The type was capable of conducting nighttime ASW operations, albeit these usually posed considerable difficulty for the flight crew.

[35][36] The Sea King also performed various other roles and missions such as search-and-rescue, transport, anti-shipping and airborne early warning operations.

[41][42] During the Vietnam War, SH-3s rescued the crews of downed aircraft at sea and over land, typically being equipped with self-sealing fuel tanks, multiple machine guns and heavy armor when performing such missions.

[43] Due to the type's greater range and the safety of having two engines, it was often used during rescue sorties into North Vietnam to retrieve downed aircrew.

[47][48] In 1992, the US Justice Department sued Sikorsky over allegations of overcharged component pricing and deliberately misleading US Navy negotiators.

[49] In 1997, the Justice Department issued further accusations against Sikorsky of willful overcharging on a contract to upgrade the Navy's Sea Kings.