The Sikorsky S-58 was developed as a lengthened and more powerful version of the Sikorsky (model S-55) or UH-19 Chickasaw, with a similar nose, but with a tail-dragger rear fuselage and landing gear, rather than the high-tail, 4-post pattern. It retained the nose-mounted piston engine with the drive shaft passing through the cockpit placed high above the cargo compartment.

The aircraft first flew on 8 March 1954. The first production aircraft was ready in September and entered in service for the United States Navy initially designated HSS-1 Seabat (in its anti-submarine configuration) and HUS-1 Seahorse (in its utility transport configuration) under the U.S. Navy designation system for U.S. Navy, United States Marine Corps (USMC) and United States Coast Guard (USCG) aircraft. The U.S. Army and Marine Corps, respectively, ordered it in 1955 and 1957. Under the United States Army's aircraft designation system, also used by the United States Air Force, the helicopter was designated H-34. The U.S. Army also applied the name Choctaw to the helicopter. In 1962, under the new unified DoD aircraft designation system, the Seabat was redesignated SH-34, the Seahorse as the UH-34, and the Choctaw as the CH-34.

Roles included utility transport, anti-submarine warfare, search and rescue, and VIP transport. In it standard configuration transport versions could carry 12 to 16 troops, or eight stretcher cases if utilized in the MedEvac role, while VIP transports carried significantly fewer people in significantly greater comfort.

A total of 135 H-34s were built in the U.S. and assembled by Sud-Aviation in France, 166 were produced under licence in France by Sud-Aviation for the French Air Force, Navy and Army Aviation (ALAT).

The CH-34 was also built and developed under license from 1958 in the United Kingdom by Westland Aircraft as the turbine engined Wessex which was used by the Royal Navy and Royal Air Force. The RN Wessex was fitted out with weapons and ASW equipment for use in an antisubmarine role. The RAF used the Wessex, with turboshaft engines, as an air/sea rescue helicopter and as troop transporter. Wessexes were also exported to other countries and produced for civilian use.

Variants

H-34A

U.S. Army version of the HSS-1 powered by a 1,525 hp R-1820-84, re-designated CH-34A in 1962, 359 built and 21 transferred from the U.S. Navy.

JH-34A

Designation for H-34A used for weapon tests.

VH-34A

Staff transport conversions of H-34A.

H-34B

H-34As converted with detail changes, became CH-34B in 1962.

H-34C

H-34B design with detail changes converted from H-34As, became CH-34C in 1962.

JH-34C

Designation for CH-34C used for weapon tests.

VH-34C

Staff transport conversions of CH-34C.

HH-34D

Designation applied to aircraft given USAF serials to be transferred under MAP and MDAP.

LH-34D

HUS-1L re-designated in 1962

UH-34D

HUS-1 re-designated in 1962 and 54 new build.

VH-34D

HUS-1Z re-designated in 1962

UH-34E

HUS-1A re-designated in 1962

HH-34F

HUS-1G re-designated in 1962

YSH-34G

YHSS-1 re-designated in 1962

SH-34G

HSS-1 re-designated in 1962

SH-34H

HSS-1F re-designated in 1962

YSH-34J

YHss-1N re-designated in 1962

SH-34J

HSS-1N re-designated in 1962

UH-34J

SH-34J without ASW equipment for cargo and training purposes.

HH-34J

Ex-USN UH-34Js operated by the U.S. Air Force

VH-34J

Staff transport conversions of SH-34J.

XHSS-1 Seabat

Three Sikorsky S-58s for evaluation by the U.S. Navy, re-designated YHSS-1 then YSH-34G in 1962.

HSS-1 Seabat

Production Anti-Submarine model for the U.S. Navy, re-designated SH-34G in 1962, 215 built

HSS-1F Seabat

One HSS-1 re-engined with two YT-58-GE as a flying test bed, re-designated SH-34H in 1962.

YHSS-1N Seabat

One HSS-1 converted as the HSS-1N prototype, re-designated YSH-34J in 1962.

HSS-1N Seabat

Night/Bad weather version of the HSS-1 with improved avionics and autopilot, re-designated SH-34J in 1962, 167 built (an addition 75 HSS-1 airframes were built to CH-34C standard for West Germany).

HUS-1 Seahorse

Utility transport version of the HSS-1 for the U.S. Marine Corps, re-designated UH-34D in 1962, 462 built

HUS-1A Seahorse

Forty HUS-1s fitted with amphibious pontoons, re-designated UH-34E in 1962.

HUS-1G Seahorse

United States Coast Guard version of the HUS-1, re-designated HH-34F in 1962, six built.

HUS-1L Seahorse

Four HUS-1s converted for antarctic operations with VXE-6, re-designated LH-34D in 1962.

HUS-1Z Seahorse

Seven HUS-1s fitted with VIP interior for the Executive Flight Detachment, re-designated VH-34D in 1962.

S-58

Commercial designation for basic cargo variant

S-58B

Commercial designation for improved cargo variant

S-58C

Commercial passenger transport/airliner version

S-58D

Commercial airliner/freighter version

S-58T

Commercial conversion to turboshaft power by Sikorsky, Orlando Helicopter, and California Helicopter. Kit uses Pratt & Whitney Canada PT6T-3 Twin-Pac turboshaft with special nose cowling featuring distinctive twin rectangular air intakes.

S-58 Heli-Camper

Commercial conversion, fitted with a Wright Cyclone R-1820-24 engine.

Orlando Airliner

Commercial conversion. 18-seat passenger transport helicopter.