The H-34 series was another successful Sikorsky design for a multi-role helicopter that improved upon the earlier H-19. It was originally conceived as an anti-submarine platform, entering service as the Seabat as well as the Seahorse in Marine service (where it was used as a naval utility transport). In US Army service, they were used as assault helicopters and known as the Chocktaw. Superficially, the H-34 resembled the H-19, albeit with a lengthened fuselage. It retained its predecessor's unconventional nose-mounted engine but replaced the four-wheel landing gear with a tail-dragging three-wheel configuration. As was the case with the H-19, the drive shaft passed through the two-crew cabin, which was located above the cargo compartment. As a transport, it could carry 12-16 troops or eight stretchers, and could also be accommodated as a VIP transport. Despite its capabilities, it was initially not used in Vietnam until pressure from the USMC pressed it into service. It did see significant action in Algeria, where Sud-built French units were in widespread service. It was also built in the UK by Westland and known as the Wessex (described separately) where it was in action during the Falklands. Overall, it served with nearly two dozen countries including NATO allies Belgium, Canada, West Germany, Italy as well as Israel (where it also saw combat) and Japan. It was eventually replaced in US service by the UH-1.

First flight of the XHSS-1 (company designation S-58) took place on 8 March 1954. It entered service with the US Navy as the HSS-1 Seabat ASW platform, as well as the HUS-1 Seahorse as a utility transport for the USMC and USCG. A night/bad weather upgrade was the HSS-1N, while transports with pontoons were known as the HUS-1A. The HUS-1L was an Antarctic version and the HUS-1Z a VIP transport. The first US Army version was the H-34A Chocktaw, some of which were former naval units, these were followed by the H-34B, -C and -D. After 1962, ASW versions were redesignated SH-34, utility versions became UH-34, USCG rescue versions HH-34, and US Army transports CH-34. With regards with foreign users, Canadian versions were designated CH-126 while Westland-built versions for the UK were known as the Wessex.