Marine squadron HMR-161 reached Korea on 2 September 1951 with 15 HRS-1s and immediately set about proving what transport helicopters could do. In Operation Windmill I on 13 September it carried 74 Marines and 18,848 lb of gear to a ridgeline in the Punchbowl area. A week later it shuttled 224 men of a reconnaissance company and 17,772 lb of supplies onto a remote hilltop, an operation American newspapers reported widely as the first helicopter troop landing in combat. In Operation Haylift II, from 23 to 27 February 1953, the squadron lifted 1.6 million lb of cargo to resupply two regiments. It operated into hot landing zones without losing a single helicopter to enemy fire, reported 90 per cent availability, and moved rocket launcher batteries twice a day so their dust plumes could not be ranged by enemy guns. One HRS-1 reportedly flew home after losing 18 inches of a rotor blade to a tree.

The Air Force’s 3rd Air Rescue Squadron, flying H-5s and H-19s, evacuated more than 7,000 wounded and rescued 170 pilots from behind enemy lines and from the Yellow Sea. The Army arrived late, after overcoming Air Force objections to it owning heavy helicopters: the 6th Transportation Company flew its first mission in March 1953, when ten H-19Cs made 30 round trips to deliver 33,925 lb of food, ammunition and charcoal to troops of the 3rd Infantry Division cut off by floods. In June 1953 Army and Marine helicopters together moved 800 South Korean troops in the largest helicopter operation of the war.

Westland, already building the S-51 as the Dragonfly, signed a licence for the S-55 on 15 November 1950. Converting it to British standards took time, and the early Whirlwinds, with American Wasp and Cyclone radials, struggled in heat and altitude: five sent to Malaya in 1954 were withdrawn within months. The Royal Navy’s 848 Naval Air Squadron took the first HAR.1s from July 1954, and Royal Navy Whirlwinds flown from HMS Ocean and Theseus helped carry troops ashore at Port Said in November 1956, one of the first ship-borne helicopter assaults.

The Alvis Leonides Major radial powered the Series 2, including the HAS.7, Britain’s first front-line anti-submarine helicopter: it could carry either a dipping sonar or a torpedo but not both, so sonar “Hunters” worked with torpedo “Killers”. The answer to the power problem was the Gnome turboshaft. The turbine HAR.10 first flew on 28 February 1959, and No. 225 Squadron became operational with it on 4 November 1961. Westland built 68 new HAR.10s and HC.10s and re-engined older airframes. Painted yellow, they became the face of RAF search and rescue around the British coast, while HC.10s served in Borneo and the Mediterranean. The last unit, No. 84 Squadron in Cyprus, gave up its Whirlwinds for Wessex in March 1982, after 21 years of turbine Whirlwind service. More than 400 Whirlwinds were built, about a hundred of them for export.

• YH-19: five Air Force service-test aircraft, first flight 10 November 1949.
• H-19A / UH-19A: Air Force utility, 600 hp R-1340; SH-19A / HH-19A rescue.
• H-19B / UH-19B: Air Force, 700 hp Wright R-1300, drooped tail boom; 264 built; SH-19B / HH-19B rescue.
• H-19C and H-19D: Army Chickasaw, 72 and 281 built (UH-19C, UH-19D after 1962).
• HO4S-1, HO4S-3: Navy utility and anti-submarine, later UH-19F; HO4S-1G, HO4S-3G: Coast Guard rescue, later HH-19G.
• HRS-1, HRS-2, HRS-3: Marine Corps assault transports, the HRS-3 becoming the CH-19E.
• S-55, S-55B, S-55C, S-55D: commercial and export models; S-55T and five-blade S-55QT turbine conversions.
• SNCASE S-55: French licence production for the army, navy and air force.
• Mitsubishi S-55C: over 40 for the Japan Self-Defence Forces.
• Westland Whirlwind: Series 1 (HAR.1 to HAR.4, American radials), Series 2 (HAR.5, HAS.7, HCC.8, Alvis Leonides Major), Series 3 (HAR.9, HAR.10, HC.10, HCC.12, Gnome turboshaft).

The S-55 was conceived when helicopters were notorious for their maintenance hours, and Sikorsky attacked the problem directly. The clamshell nose doors exposed the engine at ground level; the rotor head and main gearbox came out as one quick-change unit; and a full change of engine, clutch, gearboxes and rotor heads could be done in as little as five hours elapsed time. Marine squadron HMR-161 reported 90 per cent aircraft availability in Korea, a remarkable figure for the time.

Its costs were still those of a big piston engine: aviation petrol by the drum and regular overhauls. That is why later operators converted surplus S-55s to turbine power, from the Whirlwind HAR.10 to the civil S-55T, which shed 900 lb of empty weight with its Garrett turboshaft. No military operator published a cost per flight hour, so the table gives only a hedged estimate.