Sikorsky HO4S-3 (S-55) Helicopter


The Sikorsky S-55 was known in its RCN configuration as  HO4S-3 and nicknamed "Horse". It was a carrier-borne or shore based anti-submarine or rescue/utility helicopter. The fuselage was of an aluminum/magnesium semi-monocoque construction with a three bladed main rotor (53 ft.) and a single two bladed anti-torque tail rotor. At least 40 countries used military variants of the S-55 which had equal usage in both military and civil roles. Over its service life, production totalled over 1,700 units. First introduced in 1949, the S-55 soldiered on until 1976 in military service when the last one was retired from the Royal Navy.

2002: This  HO4S-3, serial Number 55885, is on display in hangar # 1 at the Shearwater Aviation Museum. It  was delivered to the Shearwater Naval Air Station on 31 August 1955 and was initially assigned to Squadron HS-50, where a large day-glow orange “7” was painted on the nose and sides of the aircraft 

Each leg of the quadracycle undercarriage had its own shock absorber for maximum stability during take-off and landing and manoeuvres on the ground. Floats could also be fitted to the legs for emergency landings on water, or the undercarriage could be replaced by permanent metal amphibious landing gear. (Photographer unknown)


Unless otherwise noted, these specs we taken from "RCN Aircraft General Information Data" , dated May 1, 1963.

Main rotor diameter: 53 ' 0"
Max. Height (To top of tail rotor blade)   : 15' 4"
Width (Blades folded): 11' 6"
Tail rotor diameter: 8' 5"
Max. weight: 7,750 pounds (6,800 lbs typical)
Service ceiling: 9,400 ft.
Maximum Speed: 115 knots (132  m.p.h). at sea level.
Cruising Speed: 75 knots  at sea level
Maximum Climb: 910 ft./min. at sea level.
Endurance: About 4.5 hours or a range of 265 nautical miles.
Engine: Curtiss-Wright R1300-3 (7 cylinder radial engine) restricted to 700 BHP at 39.5 in. of mercury.
Fuel: Uses 3-GP-25C 91/96 grade avgas stored in one forward tank of 86.6 Imp gal. and one aft tank holding 70.8 Imp gal. Both were crash resistant tanks situated beneath the cabin in the lower part of the fuselage.
Engine Oil: Uses 3-GP-320 100 grade oil; one tank of 7.8 Imp gal. capacity
Armament: Equipped with a Mk 43 torpedo launching installation on the port side exterior.
First taken on strength by the RCN: 5 December 1952.
Struck off strength: 16 May 1970.

ho4s3_dimensions_s.jpg HO4S-3 dimensions. Click on image to enlarge. From  RCN Aircraft General Information Data . Dated May 1, 1963. (Provided by Leo Pettipas).



Lt Robert Murray provides information on the HO4S-3 variants and their two roles:

"The RCN acquired thirteen HO4Sx helicopters in total. They were all built at the Sikorsky plant in Bridgeport, Connecticut and were purchased through Canadian Pratt & Whitney Aircraft Company of Longueuil, P.Q. The first RCN variant was the HO4S-2 of which three were acquired and allocated to No. 1 Naval Helicopter Flight, later to be known as Helicopter Utility Squadron Twenty-One (HU-21). These helicopters were used primarily as a plane guard during flight operations from the aircraft carriers.  The remaining ten were HO4S-3 models. Of the thirteen aircraft acquired five were destroyed due to accidents with no loss of life to the aircrew.

The three initial HO4S-2 models  noted above were fitted with an engine of 600 horsepower derated to 550. One of these, serial number 51444, was lost in an accident so the two remaining HO4S-2 were retrofitted with the larger 800 horsepower engines derated to 700. This, together with other technical improvements, brought them up to the HO4S-3 standard. Derated engines improved reliability and the reduced engine overhaul interval of 500 hours provided an additional margin of safety. This upgrade work was performed by Pratt & Whitney Canada Inc. at Longueuil, Quebec. Of the ten additional HO4S-3 helicopters purchased from Sikorsky in 1955, six were for the newly formed Helicopter Anti-Submarine Squadron Fifty (HS-50).

All RCN HO4S-3 helicopters were equipped with a Wright R-1300-3, seven cylinder nose mounted radial engine. The R-1300-3 drove a fully articulated three bladed, 53-foot diameter, main rotor through an angled drive shaft and reduction gearing and, a torque compensating, two bladed, tail rotor. The main rotor turned at about 220 RPM or roughly one-tenth the engine speed and is constant throughout the zero to 115-knot (132-mph) speed range of the helicopter. The normal cruising speed was 75 knots (82 mph) with a range of 265 nautical miles (305 statute miles).

The RCN HO4S-3 was employed in two roles - SAR (Search and Rescue) and anti-submarine warfare with each role being performed by a different Squadron. Helicopter Utility Squadron HU-21 was the first squadron commissioned, primarily for rescue duties both at sea, on Canadian aircraft carriers, and ashore. The second, Helicopter Anti-Submarine Squadron HS-50 equipped the helicopters with an AN/AQS-4 dunking sonar which was used for the underwater detection of submerged submarines.


In the SAR/Utility configuration used by squadron HU21, the HO4S-3 was equipped for two pilot operation, but only one pilot plus one crewman/hoist operator were normally carried on Search and Rescue (SAR) missions. Depending on fuel load, provision could be made in the main cabin for six seats or five stretchers. The primary item of airborne rescue equipment was a Breeze Company hoist with a 600 pound lift capacity. If, for any reason, the rescue crewman was required to assist a victim on the ground or in the water, the pilot in the right hand seat could operate the hoist from the cockpit. An electrically operated guillotine was available to the pilot or crewman to sever the hoist cable should it become fouled. The helicopter could also be fitted with an external sling which permitted the carrying of up to 2000 lbs. of external cargo. When the helicopter was engaged in over water "wet hoists", a large section of rubber matting was fitted over the cabin floor. This prevented salt water from seeping into the cabin floor and corroding the aircraft structure.

The call sign for the "duty" rescue helicopter based at Shearwater was "ANGEL" and, when embarked from the carrier as HU-21 Detachment 1, its call sign was "PEDRO" (The Flying Burro).


"As noted earlier, a second Squadron of Sikorsky helicopters was formed at HMCS
Shearwater on 4 July 1955, equipped with six HO4S-3 helicopters configured to support ASW operations. The Squadron consisted of 18 pilots and ten sonar operators. For any ASW sortie, the crew consisted of two pilots and one sonar operator. Similarity with the operation of the helicopter's ASW equipment with that carried in surface ships prompted the decision to employ sonar operators in the helicopters. For tactical and safety purposes the helicopters operated in pairs.

The HO4S-3 was fitted with an AQS-4 dunking sonar that could be lowered up to 100 feet into the ocean. Active "sonar ranging" allowed the helicopter to detect underwater targets and to direct fixed wing aircraft for attacks. In the absence of fixed wing support, the HO4S-3 was capable of carrying a Mk. 43 homing torpedo or a depth charge which could be launched from the single rack on the port side of the helicopter. A primary role of HS-50 Squadron was to develop tactics for the use of helicopters in anti-submarine warfare. A secondary role was the development of mine-clearing procedures".

Of the three man crew, the sonar man had the difficult task of picking up echoes and classifying them since many objects beneath the surface of the sea produce echoes besides submarines. Because the airborne sonar man is much more on his own than his shipborne counterpart, only the highest calibre operators were selected for this job.

The single biggest stumbling block against ASW operations was inclement weather. Night, fog and heavy seas presented major problems. All weather helicopters were yet to arrive on the scene. In particular, the lack of an artificial horizon when hovering made it impractical to hover in anything less than VFR conditions. A solution to the problem came later in the form of a hovering autopilot.


Leo Pettipas presents background information on the introduction of helicopters to the RCN.

"The US Navy was experimenting with sonar-equipped helicopters as far back as 1946, but it was not until the advent of the Sikorsky HO4S in 1950 that a rotary-winged machine large and powerful enough to accommodate sonar equipment became available.

The helicopter introduced a whole new dimension to ASW and can be regarded as a truly revolutionary innovation.  It gave the “small-ship” destroyer escort (DE), with its limited rate of speed, a whole new lease on life, as without the helicopter the DEs were severely handicapped in the age of nuclear submarines.   Its AN/AQS-4C sonar set, featuring a submersible dome that was lowered by cable into the sea, was a variation on the sonar equipment carried by surface vessels.   A burst of sound was transmitted from the dome, and any return echo was conveyed back through the dome and the cable to the operator in the aircraft hovering 15 or 20 feet above the surface of the water.  The operator could determine the bearing and range of the object producing the echo. The versatile helicopter had a distinct advantage over the surface vessel, which had to be constantly moving through the water while carrying out its search or attack; the noise of the water sweeping across the ship’s sonar dome at high speed had the effect of drowning out the received echo. At speeds of over 15 knots, the water rushing by the sonar dome would mask any returning echoes. The problem could be addressed by reducing the ship’s speed, but this was really not an option when the target was a fast Russian submarine.

Another advantage the helicopter had over the surface vessel was its invulnerability from attack by a torpedo-armed submarine: unlike a surface vessel whose hull shape and engine noise could be picked up by the submarine's own sensors, the submarine could never be able to determine the source of a helicopter's sonar bearing on itself.  Because it had no bodily contact with the water, the helicopter's movements could not be easily predicted by the submarine.  Finally, the helicopter's sensor was recoverable, unlike the sonobuoys deployed by fixed-wing aircraft. Constraints included a fairly high fatigue rate among crew members, inability to operate at night and in adverse weather, and comparatively limited range. The conventional fixed-wing aircraft remained essential to the ASW task of reaching out beyond the range of the helicopter.

In the convoy protection role, the helicopter extended the search perimeter of the surface escorts and provided close-in flanking, forward and rear screens.  Helicopter patrols generally lasted three to three and a half hours, conducted during the daylight hours.  Originally unarmed, the helicopter was limited to discovering and pinpointing the threat; it was still necessary to summon a destroyer or fixed-wing aircraft and home it onto the target for the attack.  The helicopters typically worked in teams, leapfrogging one another to remain in close contact with the submarine.  To enable the destroyers to visually identify the particular helicopter having the fix on the target, the sides and nose of the aircraft bore large fluorescent red numbers.

HS 50 went on its first operational cruise aboard HMCS Magnificent in February of 1956, and participated in the NATO New Broom V and VI trade protection exercises held that year.  In 1958, each of the HO4S-3s was fitted with a torpedo-launching installation on the port side of the fuselage, making them killers as well as hunters.  Throughout the late 1950s and on into 1960, all helicopter ASW operations were conducted from the carriers.  At the same time, something new was in the offing.

A distinctly Canadian contribution to rotary-winged ASW was manifested in its exploratory work in operating large helicopters from small ships.  In October of 1956 the frigate HMCS Buckingham, with a temporary landing pad fitted over her quarterdeck, commenced three months of trials in operating a helicopter from the platform.  In so doing, the RCN pioneered the deployment of large rotary-winged aircraft from escort vessels.

A prefabricated helicopter platform has been fitted above the quarterdeck  of the frigate HMCS Buckingham to test the feasibility of operating helicopters from anti-submarine escort vessels of this size. (DND photo DNS-16734)
These experiments culminated in the first landing of helicopter aboard a DDE, HMCS Ottawa, in October of the following year.  The aircraft involved was an H-34 helicopter provided for the purpose by the RCAF.  The trials successfully completed, it remained to fit the destroyers with decks and hangars.   Work was commenced in the late ‘50s toward design and development of a rapid securing/quick release/traversing system that would allow the landing and deck-handling of the aircraft.  This was eventually known as the "Bear trap".   The first vessel so configured went operational in the early 1960s. The helicopter had the effect of increasing the destroyer escorts’ radius of search, detection and attack. Of particular benefit would be the ability it would give a ship to deliver a longer-range strike on a target lying beyond the reach of shipborne weapons.
A HO4S-3 is standing by on the flight deck of  HMCS Magnificent. Prior to the introduction of  helicopters, other ships performed the duty of plane guard, ready to recover aircraft which ditched into the sea during takeoff or landing. (Canadian Forces photo) 


The era of the HO4S-3 in HS-50 ended in 1963 when the squadron was re-equipped with the larger and more capable Sikorsky CHSS-2 Sea King helicopter. The HO4S-3 was stricken off strength from Canadian service in 1970.

Electronics Suite
More Photos
HO4S-3 Flight Simulation
For additional information please refer to the document: Canada Aviation Museum Aircraft - Sikorsky HO4S-3 (S-55) by Robert Murray LCdr RCN (Ret'd)

Credits and References:

1) Leo Pettipas <lpettip(at)>  Associate Air Force Historian. Air Force Heritage and History 1 Canadian Air Division.
Winnipeg, Manitoba.
2) Extract from RCN Aircraft General Information Data . Dated May 1, 1963
4) Extract from Early Cold War History by Leo Pettipas
6) Flight Ops Photo
8) Crowsnest Magazine  Sept 1955 "Helicopter A/S Unit Formed"

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