Sikorsky S-58 / HSS "Seabat" / HUS "Seahorse" / CH-34 "Choctaw"


The first prototype of this widely used helicopter was designed to meet a 1952 requirement of the U.S. Navy for a larger and more up-to-date helicopter to replace the S-55 on anti-submarine patrol work. Designated XHSS-1, it flew for the first time on 8 March 1954, since when some eighteen hundred have been built for service in many parts of the world. The first production HSS-1 flew on 20 September 1954, and the type became operational in August 1955. Now designated SH-34G, it has the name Seabat and carries either dunking sonar search equipment or weapons for attacking submarines. Later Seabats are the SH-34J (previously HSS-1N) with automatic stabilisation and some equipment improvements, and the 'winterised' LH-34D (formerly HSS-1L). Examples of these three models are still in U.S. Navy service, although since their replacement by the SH-3 Sea King began, many have been converted to utility transports with UH prefixes.

The U.S. Marine Corps, with whom the S-58 is known as the Seahorse, have used the type since 1957 primarily for utility transport and for recovery duties connected with the U.S. satellite programme. The 12-passenger UH-34D and UH-34E (formerly HUS-1 and HUS-1A) are basically alike, the latter being an amphibious version with pontoons for landing on water. The VH-34D is a VIP transport. Army S-58's have the name Choctaw, the CH-34A and CH-34C differing only in the equipment carried, and have been in service since April 1955 as 16-seat transports or crane helicopters. Substantial numbers of military S-58 variants have been exported, and in mid-1967 were serving with the Federal German Army (one hundred and forty-four); the navies of Argentina (five), Brazil (five), France (twenty-six), Germany, Indonesia, Italy (eighteen), Japan (fourteen) and the Netherlands (twelve); and the air forces of Belgium (nine), Cambodia (three), Canada (four), France (one hundred and ten), Germany, Israel (twelve), Thailand (twenty) and South Vietnam (sixty). Those in French and Belgian service were manufactured in France by Sud-Aviation.

The commercial S-58B and S-58D are passenger/cargo transport helicopters comparable with their military counterparts. The 12-seat airline version, certificated by the FAA in August 1956, was built for Chicago Helicopter Airways (eight), New York Airways (three) and Sabena (eight). Production of the S-58 ended in December 1965 after one thousand seven hundred and sixty-six had been built by Sikorsky, but has since started again to fulfil additional U.S. orders and one from the Italian Navy for six SH-34J's. The turbine-engined development still being produced by Westland as the Wessex is described separately.

K.Munson "Helicopters And Other Rotorcraft Since 1907", 1968

Sikorsky S-58

Another winner for Sikorsky in the fifties was the Model S-58. The prototype was developed to meet a US Navy specification for a more advanced antisubmarine helicopter than the S-55. Designated XHSS-1, it first flew on 8 March 1954 and the first production aircraft, nicknamed "Seabat", was ready by September. The Marine Corps adopted it in 1957 as "Seahorse" and the Army in 1955 as "Choctaw". As a transport helicopter capable of carrying 18 combat equipped troops or a 1350kg load, the Choctaw was widely used in Vietnam. The Marines received about 500 of the S-58 in the utility version (HUS-1 and -1A).

In 1956, Westland acquired the license to build the S-58 and developed a turbine-engined version called the Wessex. Sikorsky continued producing the S-58 with the Wright radial engine; a turbine-powered conversion with a PT6T-6 Twin Pack did not become available until 1970.

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

Sikorsky S-58

The H-34 was originally developed to meet a Navy requirement for a single-engined medium helicopter that could replace the Sikorsky HO4S (S-55 / H-19) in the anti-submarine warfare (ASW) role. Designated the Model S-58 by Sikorsky and XHSS-1 by the Navy, the new aircraft incorporated several features that had first appeared on the S-55, including a nose-mounted engine and a cockpit located above and slightly forward of a spacious, box-like passenger/cargo compartment. However, the S-58 was larger and heavier than its predecessor, with a more powerful 1525hp engine and a completely redesigned, downward-sloping tail section. The S-58 also differed from the S-55 in having larger-diameter, four-bladed main and tail rotors and three-point, tail-wheel landing gear.

The prototype XHSS-1 made its first flight in March 1954, and the type entered regular Navy service in August 1955 as the HSS Seabat. A troop transport variant was simultaneously acquired by the Marine Corps as the HUS Seahorse, and one example of this type was loaned to the Army for service test and evaluation. The Army had placed preliminary orders for production H-34A troop transport variants of the Navy XHSS-1 in April 1953 and the performance of the borrowed Marine Seahorse, which was essentially identical to the H-34 version, confirmed the Army's belief that the type would be a vast improvement over the H-19s then in service.

The Army accepted the first of 437 new-construction H-34As in April 1955; an additional twenty-one HUS-1 aircraft transferred from the Marine Corps during Fiscal Year 1955 were also designated H-34A (though at least five further USMC Seahorses operated by the Army between 1955 and 1957 retained their original Navy Bureau numbers). The H-34A's performance was, as hoped, markedly superior to that of the H-19, as evidenced by the fact that in 1956 an early production example flown by Army Captains Claude E. Hargett and Ellis Hill set new world helicopter speed records on courses of 100, 500 and 1000km. The H-34A was also the first helicopter judged safe enough for routine use by the U.S. President, and in 1957 the Army organized an Executive Flight Detachment equipped with specially modified Choctaws. These aircraft were fitted with extensive soundproofing, plush VIP interiors, and upgraded communications equipment, and were designated VH-34A.

In 1960 Sikorsky began modifying Army H-34As (and Air Force H-34As and -Bs) to -C model standard through the addition of automatic flight stabilization systems and other detail changes. By January 1962 the Army had 190 H-34Cs and 179 H-34As in its inventory; under the Tri-Service designation system introduced later that year the aircraft were redesignated as, respectively, CH-34C and CH-34B. Several -C model aircraft were subsequently modified to VH-34C standard for VIP transport duties.

Though the CH-34 was arguably the most capable Army transport helicopter of the early 1960s (prior to the widespread introduction of the UH-1 Iroquois), it did not see extensive Army service in Vietnam. The Army's 1962 decision to deploy the Vertol CH-21 Shawnee to Southeast Asia instead of the faster and more capable Choctaw was based on two considerations. First, in accordance with then-current Army doctrine regarding the area-standardization of aircraft types, the CH-21 was already widely deployed in the Pacific area and the continental United States, whereas all but about thirty of the Army's CH-34s were based in western Europe. It was therefore logical and logistically preferable that the CH-21, which was considered acceptable if somewhat past its prime, should be chosen for deployment to Southeast Asia. The Army's second reason for sending the Shawnee rather than the Choctaw was a somewhat negative opinion of the Choctaw's combat survivability, a belief based on French experience in North Africa. French forces had used both the CH-21 and the CH-34 in Algeria, the former flown by the Army and Air Force and the latter by the Navy, and official evaluations had indicated that the Shawnee was more likely to survive multiple hits by ground fire than was the CH-34. The French belief that the location and 'fragile' construction of the Choctaw's fuel tanks made the craft extremely vulnerable to ground fire seemed to validate the U.S. Army's decision to deploy the Shawnee to Vietnam pending the introduction into widespread service of the UH-1 Iroquois. The approximately twenty Army H-34s that did eventually reach Vietnam proved no more vulnerable than any other aircraft in the theatre, however, and ably carried out issions ranging from combat assault to aeromedical evacuation and general cargo transport. Most of these twenty aircraft were turned over to the South Vietnamese during the course of the war, though a few were ultimately reclaimed by the Army prior to the final collapse of the Saigon Government.

The CH-34 Choctaw remained in frontline Army service well into the late 1960s, and was standard equipment in many Army Reserve and National Guard aviation units for considerably longer. Indeed, the last Choctaw was not officially retired until the early 1970s, by which time the type's duties had been divided between the UH-1H Iroquois and the CH-47 Chinook.

S.Harding "U.S.Army Aircraft since 1947", 1990

Sikorsky S-58 / HSS

Designed to overcome the range and offensive payload deficiencies of the anti-submarine HO4S version of the S-55, the Sikorsky S-58 was developed to a US Navy order for a prototype XHSS-1 placed on 30 June 1952. The nose engine position was retained for the 1137kW Wright R-1820 engine, but a completely new fuselage, four-bladed main and tail rotors, and transmission system were introduced, together with main rotor and rear fuselage folding to facilitate shipboard stowage. The prototype flew on 8 March 1954, followed by the first production HSS-1 Seabat (later SH-34G) on 20 September, and the type began to reach anti-submarine squadrons in August 1955. The HSS-1N (SH-34J) was developed for night operations, equipped with Doppler for navigation, automatic stabilisation and automatic hover coupler, while a single HSS-1F (SH-34H) flown on 30 January 1957, was powered by two General Electric T58 turboshafts. In 1960 five HSS-1Z (VH-34D) helicopters joined the Executive Flight Detachment for Presidential and VIP transport duties. Seabats stripped of ASW equipment for utility duties were designated UH-34G and UH-34J.

The US Marine Corps ordered the HUS-1 Seahorse (UH-34D) version on 15 October 1954; able to carry 12 Marines, this variant entered service in February 1957. Four HUS-1L (LH-34D) helicopters were modified for operation in the Arctic, while inflatable flotation gear identified the US Marines' HUS-1A (UH-34E) and the US Coast Guard's HUS-1G (HH-34F). The US Army ordered several hundred H-34A, H-34B and H-34C Choctaw helicopters powered by 1063kW R-1820-84 engines and each carrying 16 troops or eight stretchers in the medevac role, the first unit being equipped in September 1955. The type was exported widely and built under licence in France and the UK, the turbine-powered Westland product known as the Wessex. In April 1971 Sikorsky received FAA approval for the S-58T PT6A Twin Pac-powered turbine conversion for H-34 airframes. One hundred and forty-six conversions, or conversion kits, were produced until, in 1981, the rights were sold to California Helicopter International. Since then customers for the California Helicopter (Sikorsky) S-58T included New York Airways, the Indonesian and South Korean air forces (now retired) and the government and air force of Thailand. The S-58T is also in service in Argentina with the Presidential Aircraft Squadron. Small numbers were built of S-58B and S-58D civil passenger and cargo transport helicopters, a 12-seat airline version being operated by Chicago Helicopter Airways, New York Airways and SABENA. When production was terminated in January 1970, Sikorsky had manufactured a total 1,820 S-58s of all versions.

In addition to the California Helicopters version, Orlando Helicopters also offers S-58 conversions. An S-58 Heli-Camper, similar in fit to the OHA-S-55 Heli-Camper is available, powered by a Wright Cyclone R-1820-84 engine. A further Orlando S-58T conversion is the Orlando Airliner, an 18-seat all-passenger version with nine additional tinted windows fitted on each side of the cabin. Thus far, nearly 30 conversions have been completed.

D.Donald "The Complete Encyclopedia of World Aircraft", 1997

Developed to meet US Navy specification for more advanced anti-submarine helicopter. Designated XHSS-1, it made its first flight 8 March 1954; first production aircraft, nicknamed Seabat, flew 20 September 1954. The army and navy versions were generally similar, differing mainly in equipment and fuel capacity. Westland acquired licence to build S-58 in the UK in 1956 and developed turbine version under name of Wessex. Total of 166 also produced under licence by Sud-Aviation in France. First commercial deliveries of S-58C made in 1956-57. In January 1970, Sikorsky announced the design of kits for the conversion to turbine power by the installation of the Pratt & Whitney PT6 Twin-Pac. First flight of the S-58T took place 19 August 1970; FAA certification awarded April 1971. Total of 153 conversion kits manufactured by Sikorsky, but exclusive rights acquired by California Helicopter International in 1981.


CH-34A/H-34A Choctaw: Transport and general purpose helicopter for US Army.

CH-34C (formerly H-34C) Choctaw: Similar to CH-34A, but with airborne search equipment.

LH-34D (HSS-1L) : Winterised version of Navy Seabat.

SH-34G (HSS-1) Seabat: Anti-submarine version ordered by US Navy 30 June 1952; accepted for service in February 1954.

SH-34J (HSS-1N) Seabat: Improved version of SH-34G.

UH-34D (HUS-1) Seahorse: Utility version for Marines; ordered 15 October 1954 and accepted for service January 1957.

UH-34E (HUS-1A) Seahorse: Version with pontoons for emergency operation from water.

VH-34D (HUS-1Z) : VIP transport version of Seahorse.

S-58B: Commercial passenger/freighter version.

S-58C: Commercial passenger-carrying version with two doors on starboard side of cabin.

Description applies to this version except where indicated.

S-58D: Commercial passenger/freighter version.

S-58T: Turbine conversion with Pratt & Whitney PT6 Twin-Pac, comprising two PT6 engines and combining gearbox; improved performance includes greater speed and lifting power, and better hot-and-high operation.

Westland Wessex: Licence-produced UK version.

CUSTOMERS: Sikorsky built 1,821 models, mostly for military customers, between 1954 and 1968; another 166 built by Sud-Aviation and 356 by Westland under licence.

DESIGN FEATURES: Four-blade all-metal main and tail rotors. Blades of main rotor interchangeable. Tail rotor has servo control. Main and tail rotor brakes.

FUSELAGE: Semi-monocoque structure.

LANDING GEAR: Conventional three-wheel undercarriage, with tailwheel at extreme rear of fuselage. Air-oil shock-absorber struts. Mainwheels have rotating struts to reduce drag and weight. Tailwheel is fully castoring and self-centring, with an anti-swivelling lock. Mainwheel tyres 11.00 x 12. Tailwheel tyre 6.00 x 6. Toe-operated mainwheel brakes. Track 3.66m. Wheelbase 8.75m.

POWER PLANT: One Wright R-1820-84 radial air-cooled engine, rated at 1,136kW for take-off (S-58C) or 1,342kW PT6T-3 Twin-Pac comprising two PT6 turboshaft engines side by side with combining gearbox. Engine is mounted behind large clamshell doors in nose of fuselage to allow complete accessibility from ground level. Fuel capacity is from 750 litres to 1,164 litres depending on model.

ACCOMMODATION: Pilot's compartment above main cabin seats two side by side with dual controls. Cabin normally seats 12 passengers. Up to eight stretchers can be carried. Sliding windows of pilot's compartment removable in an emergency. Cabin and cockpit air conditioned and soundproofed.

Jane's Helicopter Markets and Systems

Technical data for Sikorsky S-58

Crew: 2, passengers: 12-18, engine: 1 x Wright R-1820 pistone engine, rated at 1137kW, main rotor diameter: 17.1m, length: 17.3m, height: 4.9m, take-off weight: 6350kg, empty weight: 3754kg, max speed: 198km/h, cruising speed: 158km/h, rate of climb: 5.6m/s, service ceiling: 2900m, range: 450km