By Lieutenant Colonel Ronald J. Brown
U.S. Marine Corps Reserve, Retired
The HRS transport helicopter was the military version of the Sikorsky S-55 commercial aircraft. It featured the familiar Sikorsky design signatures, a single overhead main rotor and a small anti-torque rotor on the tail boom. Although many of its components were simply enlarged versions of similar ones found in the HO3S, the HRS did not look much like the Marines’ earliest observation helicopter. It was much larger, its cargo space included seats for eight passengers, the two-seat cockpit was located high on the fuselage and set farther back than the HO3S, and the engine was mounted low on the front of the aircraft rather than high amidships. Although initially selected as only an interim model until a larger heavy-lift helicopter became available, the Navy Department eventually purchased 235 variants of the S-55. The U.S. Army and Air Force flew similar models as H-19s, and the Coast Guard variant was the HO4S-3G.
The Marine Corps turned to the Sikorsky S-55 after its first choice, the Piasecki H-16, outgrew the ability to operate from small escort carriers—foreseen as the transport helicopter’s primary mission. The Navy was already looking at one version of the S-55; an antisubmarine variant designated the HO4S. There was no obvious external difference between the HRS and the HO4S. This was because the main difference was each respective aircraft’s mission. The Marine transport helicopter did away with mine detection equipment but mounted troop seats and had self-sealing fuel tanks. The most innovative feature of the S-55 was its engine placement. It was set low in the helicopter’s nose. A drive shaft ran up through the back of the cockpit to provide power to the three-bladed overhead main rotor. The engine placement made it easy to reach, cutting maintenance time. That configuration also eliminated critical center-of-gravity problems that plagued both the HO3S and the HTL. The HRS also mounted a drop hook to carry external loads under the cabin. The main shortfalls of the HRS were that the machine was underpowered and mechanical failures required them to be grounded on several occasions. No Marine HRSs were lost to enemy fire, but several crashed while hovering and at least two went down in mid-air due to engine failure.
The HRS was a great step forward, but it was not the transport helicopter Marine planners envisioned. They wanted an aircraft that could carry 15 or more men to ensure unit integrity during assaults and generating enough lift to carry most division equipment. The main problem with the HRS was lifting power. Although rated for eight passengers, in the harsh reality of the Korean mountains the HRS could only carry about six men—only four if they were fully combat loaded. Both Igor Sikorsky and Frank Piasecki worked feverishly to deliver a more capable aircraft, but that advance would have to wait until the development of a practical turbine helicopter engine.
The first batch of Marine HRS-1s included 60 machines and the second order of HRS-2s mustered 91, the final version (HRS-3) included 89 more. Only the first two variants saw action in Korea, but some HRS-3s were still in the Marine inventory when their designation was changed to the CH-19E in accordance with the Department of Defense unified designation system in 1962.
Manufacturer: Sikorsky Aircraft Division of United Aircraft Corporation
Type: Transport helicopter
Accommodation: Ten-places (two crew and eight passengers)
Power Plant: One 600 hp Pratt & Whitney R-1340-57
Cruising speed: 80 mph
Payload: 1,050 pounds