The Sikorsky SH-3 Sea King (company designation S-61) is an American twin-engine anti-submarine warfare (ASW) helicopter designed and built by Sikorsky Aircraft. A landmark design, it was one of the first ASW rotorcraft to use turboshaft engines.Leoni 2007, p. 251.
The Sea King has its origins in efforts by the United States Navy to counter the growing threat of Soviet submarines during the 1950s. Accordingly, the helicopter was specifically developed to deliver a capable ASW platform; in particular, it combined the roles of hunter and killer, which had previously been carried out by two separate helicopters. 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. In late 1961 and early 1962, a modified U.S. Navy HSS-2 Sea King was used to break the FAI 3 km, 100 km, 500 km, and 1000 km helicopter speed records. 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. As of 2024, many examples of the type remain in service in nations around the world, although some major users have begun to retire the type. The Sea King has been built under license by Agusta in Italy, Mitsubishi in Japan, Canada by United Aircraft of Canada, and by Westland in the United Kingdom as the Westland Sea King. The major civil versions are the S-61L and S-61N. 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.
Development Origins During the Cold War, the Soviet Navy built up a large and varied fleet of submarines which at one point was in excess of 200 operational submarines. The US Navy countered this threat by the improvement and development of various anti-submarine warfare (ASW) capabilities, which resulted in the development of the Sea King.Fieldhouse and Taoka 1989, pp. 70–71, 74. 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. Sikorsky received a request from the service to design a new turbine-powered helicopter that would be capable of performing the ASW mission. The specification included a dipping sonar, mission endurance of four hours, and the ability to support a weapons load of .Mutza 2010, p. 106.
In 1957, Sikorsky was awarded a contract to produce an all-weather amphibious helicopter for the US Navy. As per the earlier specification, this new rotorcraft was to excel at ASW; specifically, it would combine the roles of hunter and killer, as these two duties had previously been carried out by two separate helicopters.Chant 1988, p. 464. It was also the first helicopter to be procured under the US Navy's new weapon system concept, under which Sikorsky was responsible not only for the design and production of the airframe, but all major onboard systems, such as the sonar, navigational equipment, electronic devices, and support equipment. As such, the navigation suite for the rotorcraft was developed jointly by Sikorsky and the US Navy."HSS-2." Flight International, 15 May 1959. p. 696.
Key features of the emerging ASW helicopter included its amphibious hull, which enabled the rotorcraft to readily perform water landings, and its adoption of a twin-turboshaft engine arrangement that enabled it to be larger, heavier and better-equipped than had been possible with prior helicopters. 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. A total of ten prototypes were produced to support the development program.Mutza 2010, p. 107.
Into flight
On 11 March 1959, the first prototype conducted its maiden flight. During early 1961, a pair of prototypes were stationed on board the aircraft carrier to fulfill a demand for carrier suitability trials. These trials, which involved testing the folding mechanism of the main rotor blades and a series of takeoffs performed during winds of up to , were completed successfully in mid-1961."HSS-2 Completes Carrier Trials." Naval Aviation News, July 1961, pp. 22–23. 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.Frawley 2003, p. 194.
In late 1961 and early 1962, a modified US Navy HSS-2 Sea King was used to break the FAI 3 km, 100 km, 500 km and 1000 km helicopter speed records. This series of flights culminated on 5 February 1962 with the HSS-2 setting an absolute helicopter speed record of ."USN HSS-2's 200 m.p.h." Flight International, 15 February 1962. p. 233. This record was broken by a modified French Sud-Aviation Super Frelon helicopter on 23 July 1963 with a speed of .
Further developments
The base design of the Sea King had proved sound and several aspects were judged to be potentially useful for other operators, and Sikorsky elected to pursue the further development of the rotorcraft for other markets beyond the US Navy. One of the major variants of the Sea King to be produced was a model for civil operators, which was designated as the Sikorsky S-61L. The first operator of the S-61L was Los Angeles Airways, who introduced the type to service on 11 March 1962.Apostolo, G. "Sikorsky S-61".The Illustrated Encyclopedia of Helicopters. Bonanza Books, 1984. ."The Self-Supporting Helicopter" Time Magazine. 26 December 1960. 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.Apostolo, Giorgio. "Sikorsky S-61R". The Illustrated Encyclopedia of Helicopters. New York: Bonanza Books. 1984. .
In U.S. Navy service, the initial SH-3A model of the Sea King would be progressively converted into the improved SH-3D and SH-3H variants; these featured more powerful engines and improved sensors that gave the type greater operational capabilities as an ASW platform. 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. 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.Williamson 2000, pp. 149, 167.
The NH-3A (S-61F) was an experimental high-speed compound helicopter based on the Sea King tested in the 1960s. Later modified with a tail rotor able to rotate 90° to serve as a pusher propeller; this helicopter demonstrated "Roto-Prop" pusher propeller for Sikorsky's S-66 design.Leoni 2007, pp. 26–28. A minesweeper version of the Sea King for the U.S. Navy was made, with nine converted from SH-3A aircraft and then called the RH-3A.
In addition to those Sea Kings that were manufactured by Sikorsky, several license agreements were enacted with other firms to produce the type. These included the Japanese conglomerate Mitsubishi and the Italian aerospace company Agusta. Another licensee was the British helicopter manufacturer Westland Helicopters, which substantially redesigned the Sea King to produce various models of their own, collectively referred to as the Westland Sea King.Uttley 2001, p. 206.McGowen 2005, p. 119.Thorn and Frawley 1998, p. 164. In contrast to the US Navy's Sea Kings, the Westland Sea King was intended for greater operational autonomy.Lake 1996, pp. 114–115. In total, Westland produced 330 Sea Kings; outside of its British-based operators, various export customers were found for the Westland Sea King. including the Indian Naval Air Arm, the German Navy, the Royal Australian Navy, and the Royal Norwegian Air Force.McGowen 2005, pp. 120, 126.
While Sikorsky opted to terminate its own Sea King production line during the 1970s, the type has had a lengthy service life. In September 2009, it was reported that nearly 600 Sea Kings were believed to still be operational.Baruzzi, Cara. New Haven Register, 6 September 2009.
Design The Sikorsky SH-3 Sea King is a twin-engine medium-sized amphibious rotorcraft. Many of the features on board the Sea King represented a considerable advancement over preceding helicopters. In addition to being fully amphibious and capable of operating under all weather conditions, it is the first operational American helicopter to be able to simultaneously hunt and destroy submarines. Its twin-turboshaft powerplant layout gave the SH-3 a higher payload and greater reliability than previous anti-submarine helicopters. In the event of a single engine failing, the Sea King could continue flying on a single engine.Bishop and Chant 2004, p. 208. The powerplant used on the Sea King was the General Electric T58-GE-8B, which was initially capable of generating up to each.
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. When conducting anti-submarine missions, the rear aircrew operated the aircraft's sensors and interpreted the generated data.Williamson 2000, p. 169. For search-and-rescue missions, the Sea King's cabin could accommodate up to 22 survivors. In a medical layout, a maximum of nine stretchers plus two medical officers could be carried. In the troop transport role, up to 28 soldiers can be accommodated."HSS-2." Flight International, 15 May 1959. p. 697.
The Sea King features many design elements to support naval-orientated operations. The main rotor blades and the tail section can be folded via fully automated systems for storage on board ships. 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. Deployable airbags in the aircraft's sponsons added to the rotorcraft's stability and buoyancy, resisting pitching and rolling.Jackson 2005, p. 207. The hull design was compatible with landing on challenging terrain, including ice, snow, swamp land, and tundra. Wheels are installed in the sponsons for land operations.