By Lieutenant Colonel Ronald J. Brown
U.S. Marine Corps Reserve, Retired
The HO5S helicopter, developed from Sikorsky’s S-52 design begun in 1948, was the purpose-built replacement observation helicopter for the HO3S. The S-52 was first conceived as a compact two place machine, but it eventually incorporated recommendations from the fighting front under the designation S-52-2. The HO5S was more compact than its predecessor and featured several new design features to overcome technical problems identified in the HO3S. Forty-eight HO5S-1s were ordered for the Marine Corps in 1951 and accession began in January 1952.
Although its theoretical performance statistics appear only marginally better than its predecessor, the HO5S was actually a much-improved aircraft that addressed many of the HO3S’s shortcomings. The HO5S was the first U.S. helicopter fitted with all-metal blades, could mount two stretchers internally, and was much more stable on the ground due to its low center of gravity and four-wheel landing gear. The most unique practical innovation was a hinged, two-piece, forward-mounted observation bubble. Opening the left seat side of the bubble allowed access to the cabin interior for two stretcher-borne patients. In addition, the HO5S could carry three combat-loaded men over short distances.
By the time of the armistice in 1953, almost all VMO-6 helicopters were HO5Ss. Unfortunately, plans to replace light airplanes with HO5S helicopters in Marine observation squadrons had to be put on hold due to performance problems and structural defects that came to the fore in Korea. It was decided that the Marine Corps needed a machine that offered better stability and easier inflight control in addition to a more powerful engine. Thus, instead of becoming the backbone of Marine observation squadrons, the HO5S was actually replaced by the Kaman HOK beginning in 1954; the later aircraft remained in operational service for the next decade until was it in turn replaced by the Bell UH-1 Iroquois (“Huey”), which remains the designated Marine observation and utility helicopter to this day. Marine observation squadrons were equipped with fixed-wing airplanes after light helicopter squadrons were created during the Vietnam-era.
Manufacturer: Sikorsky Division of United Aircraft Corporation
Power Plant: 245 hp Franklin O-425-1 engine
Dimensions: Length, 27’ 5”; height, 8’8”; rotor, three 33’ metal blades
Performance: Cruising speed, 96 mph
Lift: Pilot and three passengers or two internal stretchers