The Sikorsky H-34 (company designation S-58) is an American piston-engined military utility helicopter originally designed by Sikorsky as an anti-submarine warfare (ASW) aircraft for the United States Navy. A development of the smaller Sikorsky H-19 Chickasaw (S-55), the H-34 was originally powered by a radial engine, but was later adapted to turbine power by the British licensee as the Westland Wessex and by Sikorsky as the S-58T. The H-34 was also produced under license in France by Sud Aviation.

The H-34 was one of the first successful military utility helicopters, serving on every continent with the armed forces of 25 countries. It saw combat in the Dominican Republic, Nicaragua, the Six-Day War, the Vietnam War, and the Algerian War, where the French Air Force used it to pioneer modern air assault tactics. It was the last piston-engined helicopter to be operated by the United States Marine Corps (USMC), having been replaced by turbine-powered types such as the UH-1 Huey and CH-46 Sea Knight; in the USMC, the H-34 was often called the "HUS" after its original designation in that service. A total of 2,340 H-34s were manufactured between 1953 and 1970, including the license productions in the UK and France.