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The Sea King has its origins in efforts by the United States Navy as a means of counteracting the growing threat of Sovietsubmarines 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 re-designated 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. Several Sea Kings, operated by the United States Marine Corps's HMX-1 unit, are used as the official helicopters of the President of the United States, for which the call sign "Marine One" would be used.
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 2015, many examples of the type remain in service in nations around the world. The Sea King has been built under license by Agusta in Italy, Mitsubishi in Japan, and by Westland in the United Kingdom as the Westland Sea King. The major civil versions are the S-61L and S-61N.
XHSS-2 Sea King prototype
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. During the late 1950s, the US Navy took advantage of advances in turboshaft engines by commissioning a sizable navalised helicopter. Sikorsky received a request from the US Navy to design a new turbine-powered helicopter 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 380 kg (840 lb).
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 helicopter was to excel at ASW. In particular, it would combine the roles of hunter and killer, as these duties had previously been carried out by two separate helicopters. 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.
Key features of the emerging ASW helicopter would include its amphibioushull, enabling the rotorcraft to readily perform water landings, and the adoption of a twin-turboshaft engine arrangement that enabled a larger, heavier and better-equipped aircraft than was possible with prior helicopters. The designation HSS-2 was applied 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. In March 1959, the first prototype conducted its maiden flight.
In early 1961, a pair of prototypes were stationed on board the aircraft carrierLake Champlain 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 50 MPH, were completed successfully in mid-1961. Shortly after the competition 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. Upon entering service, it was not only the largest amphibious helicopter in the world, but also held the distinction of being the first all-weather rotorcraft to reach production status for the US Navy.
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 210.6 mph. This record was broken by a modified French Sud-AviationSuper Frelon helicopter on 23 July 1963 with a speed of 217.7 mph.
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 Sea King 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. Another noteworthy Sea King variant, the significant change this time being the adoption of a conventional hull, 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.
In US 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.
The Royal Canadian Navy (RCN) became a major operator of the type (see Sikorsky CH-124 Sea King) following its introduction to service in 1963, and remained as Canada's dominant maritime helicopter for 50 years, until 2018.  One notable innovation in Canadian operations, which was subsequently adopted by several other nations, was the use of a winch 'hauldown' landing and securing method, referred to as a 'Beartrap'. This device considerably increased the ability of Sea Kings to land in difficult conditions, such as on small flight decks or during poor weather conditions.
In the early 21st century, following their drawdown in US service, there have been a number of initiatives to refurbish ex-military Sea Kings for continued operations; in addition to civil operators, nations such as Egypt and India acquired refurbished former US Sea Kings to supplement their own aging fleets. While Sikorsky had ended production of the type during the 1970s, it was reported that nearly 600 Sea Kings were in operational service in 2009.
SH-3A landing on the sea in 1964
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 holds the distinction of being 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. The powerplant used on the Sea King was the General Electric T58-GE-8B, which was initially capable of generating up to 1,250 shp 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. 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.
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 onboard ships. The adoption of an amphibioushull 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. 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.
The armament fitted upon a Sea King could vary considerably. For anti-submarine missions, the aircraft could carry up to four torpedoes or four depth charges. For anti-ship duties, some models were outfitted to carry one or two missiles, typically Sea Eagles or Exocets. The Sea King could also be fitted to deploy the B57 nuclear bomb. ASW equipment used on Sea Kings has included the AQS-13A/B/E dipping sonar which included specialized computers for processing sonar and sonobuoy data, various models of sonobuoys, ARR-75 Sonobuoy Receivers, and the ASQ-81 Magnetic Anomaly Detector. The commonly fitted AKT-22 data link enabled the rapid dissemination of sonar information to other friendly elements. Some later Sea King models featured the TACNAV digital navigation system (first generation GPS) and overhauled cockpit instrumentation for night vision compatibility.
Several UH-3H Sea Kings taking off, 2003
The Sea King became operational with the United States Navy in June 1961 as the HSS-2. When the unified aircraft designation system was introduced, the aircraft's designation changed to SH-3A. It was used primarily for anti-submarine warfare: detecting and tracking Soviet submarines; in the event of an outright military conflict, they would have been used to launch attacks upon them as well. Sea Kings could also operate from offshore platforms to extend their surveillance and strike range. Nighttime ASW operations were possible, albeit posing considerable difficulty for the flight crew.
The Sea King also performed various other roles and missions such as search-and-rescue, transport, anti-shipping and airborne early warning operations. Aircraft carriers would typically deploy Sea Kings to operate near the carrier as a plane guard, ready to rescue air crew who crashed during takeoff or landing. They routinely transferred personnel and mail between vessels.
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. 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. The Sea King was also used for medical evacuations and disaster relief efforts.
Several Sea Kings, operated by the United States Marine Corps's HMX-1 unit, are used as the official helicopters of the President of the United States; in this capacity, the call sign 'Marine One' is used by the helicopter currently occupied by the President. As of 2012, a replacement helicopter fleet for the Sea King is pending under the VXX program. In 1992, the US Justice Department sued Sikorsky over allegations of overcharged component pricing and deliberately misleading US Navy negotiators. In 1997, the Justice Department issued further accusations against Sikorsky of willful overcharging on a contract to upgrade the Navy's Sea Kings.
During the 1990s, the Sea King was replaced in the ASW and SAR roles by the U.S. Navy with the newer Sikorsky SH-60 Sea Hawk. However, the SH-3 continued to operate in reserve units in roles including logistical support, search and rescue, and transport. On 27 January 2006, the SH-3 was ceremonially retired at NAS Norfolk, Virginia, by Helicopter Combat Support Squadron 2 (HC-2). They have been replaced by increasingly advanced variants of the SH-60 Sea Hawk.
Combat search and rescue helicopter for the U.S. Navy. 12 converted from SH-3A.
Military transport version for the U.S. Air Force; three converted from SH-3As into CH-3A configuration; they later became CH-3Bs.
Experimental high-speed compound helicopter, with extensive streamlining, no floats, short wings carrying two turbojet engines for extra speed; one converted from SH-3A. 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.
Minesweeper helicopter for the U.S. Navy. Nine converted from SH-3A aircraft.
VIP transport helicopter for the U.S. Army and Marine Corps; originally designated HSS-2Z. Eight built, plus two SH-3A conversions rebuilt from damaged helicopters (one YHSS-2 and one SH-3A). The rest were returned to the U.S. Navy in 1975-76 and replaced by the VH-3D.
Military transport helicopter for the U.S. Air Force.
VIP transport helicopter for the U.S. Marine Corps, 11 built. It entered service in 1976.
Cargo, utility transport helicopter for the U.S. Navy. 105 conversions from SH-3A and SH-3D.
Upgrade of the SH-3G as an anti-submarine warfare (ASW) helicopter for the U.S. Navy. It included SH-3G features with improvements for ASW, anti-ship missile detection and other airframe improvements. 163 SH-3A/D/Gs were upgraded to SH-3H configuration.
Airborne early warning version for the Spanish navy.
Cargo, utility transport version for the U.S. Navy; converted from SH-3H by removing ASW systems.
The Sea King Improvement Program (SKIP) added modernized avionics as well as improved safety features.
Alternate version of the CH-124A without a dipping sonar but formerly with a MAD sensor and additional storage for deployable stores. In 2006, the five aircraft of this variant were converted to support the Standing Contingency Task Force (SCTF), and were modified with additional troop seats, and frequency agile radios. Plans to add fast-rope capability, EAPSNIPS (Engine Air Particle Separator / Snow & Ice Particle Separator) did not come to fruition.
Six CH-124Bs were upgraded to the CH-124B2 standard in 1991-1992. The revised CH-124B2 retained the sonobuoy processing gear to passively detect submarines but was also fitted with a towed-array sonar to supplement the ship's sonar. Since anti-submarine warfare is no longer a major priority within the Canadian Forces, the CH-124B2 were refitted again to become improvised troop carriers for the newly formed Standing Contingency Task Force.
One CH-124 operated by the Helicopter Operational Test and Evaluation Facility located at CFB Shearwater. Used for testing new gear, and when not testing new gear, it is deployable to any Canadian Forces ship requiring a helicopter.
Unofficial designation for four CH-124s that were modified for passenger/freight transport. One crashed in 1973, and the survivors were later refitted to become CH-124A's.
Westland Sea King AEW.2A of the Royal Navy in 1998
Williamson, Ronald M. Naval Air Station Jacksonville, Florida, 1940-2000: An Illustrated History. Nashville, Tennessee: Turner Publishing, 2000. ISBN1-5631-1730-4.
Núñez Padin, Jorge Felix (2014). Núñez Padin, Jorge Felix (ed.). Sikorsky S-61D.4 & UH-3H Sea King. Serie Aeronaval (in Spanish). 32. Bahía Blanca, Argentina: Fuerzas Aeronavales. Archived from the original on 3 April 2015. Retrieved 2014.