Al Barbour
09-25-2002, 16:11
Big Hummer – CH-37C
When first publicly unveiled in January 1954, the Sikorsky H-37 was introduced by its manufacturer as a "giant, twin-engine transport” that represents a "tremendous advance in the art of designing and building helicopters".
In fact, the H-37 was the biggest, fastest and most powerful production helicopter in the free world until the introduction of Boeing Vertol's turbine-driven Chinook in 1961. Originally developed for the United States Marine Corps for transport of cargo and troops and for the evacuation of casualties, the H-37 had a gross weight of 31,000 pounds, more than four times that of its predecessor, the Sikorsky H-19 (S-55).
Short Development Period
After a relative short development period of only three years, the first H-37 prototype carried out its maiden flight with Sikorsky test pilot Jimmy Viner at the controls in Stratford, Connecticut, on December 12, 1953. A total of four pre-production versions, Serial No. 133732 to 133735, were built and underwent extensive evaluation under the military designation of XHR2S-1. Military production versions of the H-37 were designated by the Marine Corps as HR2S-1. The leading ‘X’ of the first four helicopters indicated that they were prototypes. Since the HR2S-1 was the second version of the transport helicopter, a ‘2’ was inserted in its name to indicate this. The Marines, being big on card playing and the ‘2’ card being called a ‘Deuce’, they nicknamed the HR2S-1 the ‘Deuce’.
The United States Army also noticed the potential of the H-37 and, in 1954, began to fly one of the four prototypes under the new designation YH-37. Later production versions were designated as H-37A. Following the Army's practice to name helicopters in honor of the American Indian tribes, they christened their H-37A the ‘Mojave’
Advanced design features...
The H-37, a very complex and advanced design helicopter, had incorporated into it many new features, such as 'clamshell' nose loading doors, similar to the Bristol 170 fixed-wing freighter, and a retractable main landing gear. It was also the first helicopter with a hydraulic main rotor blade fold system, automatic stabilization equipment (ASE), and the first twin-engine rotorcraft in U.S. military service. The airframe of the H-37 was an all-metal design consisting of the fuselage, main gearbox cowling, also referred to as the 'doghouse', stub-wings, engine nacelles, horizontal stabiliser and tail rotor pylon. The nacelles also accommodated the helicopter’s fully retractable main landing gear. The two-cell, 400-gallon capacity fuel tanks for each engine were located in the aft portion of the engine nacelles and in the adjacent stub-wing sections. This innovative arrangement made the 30-foot long cargo cabin clear for loading and unloading of troops or cargo up to a 105 mm howitzer and trailer. A cargo hatch, also referred as the ‘hellhole’, was located in the centre of the reinforced cabin floor and a cargo sling capable of carrying 10,000 pounds could be attached to hardpoints around the hellhole. In order to further assist in loading, an electric hoist, capable of lifting 2,000 pounds, was mounted on a monorail attached to the cabin ceiling.
...with Archaic engines
In contrast to its rather advanced design features, the H-37 was powered by archaic Pratt & Whitney Double Wasp R-2800 piston engines. It was used in many aircraft, including the famous Douglas DC-6 fixed-wing transport and even in World War II veterans like the Corsair and Thunderbolt.
The design of the H-37 helicopter called for the engines to be mounted in separate nacelles at the outboard end of each stub-wing, with driveshafts pointing inboard at an angle of approximately 80 degrees and upward at an angle of approximately 12.5 degrees. A hydro-mechanical clutch was splined to the output of each engine and a driveshaft connected the clutch to the main gearbox in the upper center of the fuselage. The main gearbox transferred power to the intermediate and tail rotor gearboxes and provided the correct gear reduction for the main and tail rotors.
There were two types of throttle controls in the pilot's compartment, the overhead throttle quadrant and a twist-grip throttle on each of the collective pitch controls. The quadrant throttles were used for engine starting, ground operation, clutch engagement and to synchronize the engines. Normally, during flight, the quadrant throttles were not used except for minor engine synchronization adjustments or for single-engine operation. The twist-grip throttle was used during flight and automatically synchronized the power setting of both engines whenever changes in the collective pitch occurred. The R-2800 radials powered the H-37 quite well and were very responsive to the throttles, but due to the inertia of this massive helicopter, pilots had to fly with much anticipation. It was said that maneuvers near the ground were indeed thrilling until the pilot mastered the twist grip throttle.
New World Records
In determining the maximum capabilities of the HR2S, the naval version of the H-37, two new weight lifting records and a new speed record were established at Bradley Field, Connecticut, between November 9 and 11, 1956. Piloted by Major Roy L. Anderson of the Patuxent River Naval Air Test Center and Sikorsky test pilot Robert Duke, the HR2S lifted a payload of six metric tons (13,260 pounds) to an altitude of 7,000 feet and a payload of five metric tons (11,050 pounds) to maximum altitude of 12,100 feet. The former weight record was 8,820 pounds at an altitude of 6,560 feet set in 1955 by a Russian Yakowlev Yak-24 tandem helicopter. Only one day after establishing the new records, Major Anderson reached a maximum speed of 162.743 miles per hour (142 knots) with an empty HR2S and set a new world speed record for helicopters. This topped the old speed record of 156.005 miles per hour (136 knots) set in 1954 by a turbine-driven Sikorsky XH-39 experimental helicopter.
Trials and troubles
The Marine Corps set great expectations on the brand new H-37 ‘Deuce’ which was designated as HR2S at that btime. In late 1956, Marine Corps Experimental Helicopter Squadron HMX-1, stationed at Quantico, Virginia, received its first two dark blue H-37 for squadron experimental evaluation. In the interim, new members of the Marine Medium Helicopter Squadron 461 HMH-461 attended ground school at the Sikorsky factory in Stratford Connecticut.
One of them, First Lieutenant Michael Leahy, now a retired Lieutenant Colonel, recalls, ”the first pilots came to Quantico in January of 1957 for the Fleet Introduction Program (FIP).” Awaiting them were four brand new green Deuces, serial numbers 140314 to 140318. In contrast to the already existing blue Deuces with serial numbers beginning with 138 and lacking dorsal fin at the base of the tail rotor pylon, the green Deuces were the full production configuration. The FIP was officially intended as a three-month evaluation of the HR2S helicopters under realistic conditions. According to Leahy, the squadron pilots, almost akin to test pilots, were to help weed out and correct discrepancies, which were certain to show up in the FIP. "For instance", he recalls, "there was a round main oil cooler in the original models of the Deuce, one in each engine pod. We found that they were not doing the job and the engines were overheating. Sikorsky replaced the offending coolers with more efficient square coolers which then became standard."
Another experience of Deuce pilot Leahy involved an engine clutch failure. As a senior First Lieutenant with a lot of helicopter time, compared to those who came to 461 immediately upon graduation from flight training at NAS Pensacola, he was flying with a new Second Lieutenant, doing touch-and-go landings. As they came to a hover just before touch down, the aircraft lurched rather violently down on the port side. The clutch on the port engine failed. Leahy recalls: ”I got the ship down okay, but noticed that the engine tachometer had pegged, indicating an overspeed. I quickly reached up for the offending throttle control lever on the overhead quadrant and gently pulled it back to idle. We then sat there until a crash truck arrived as a safety precaution.” A few of months earlier a Deuce burned up after a clutch failure at Quantico. ”In that instance, with a load on, the engine clutch assembly failed, causing the engine to overspeed”, recalls Leahy. ”The pilot yanked the throttle back post haste, causing a huge backfire and igniting fuel that was pouring from the punctured fuel cells, caused by flying debris from the cooling fan rotor buckets”.
Many problems of the Deuce were caused by vibration. Broken wires on the instrument panel were very common. John R. Tay, a former Deuce helicopter electrician, states that ”the biggest culprit was the automatic blade fold system. There was a switch on each blade that would indicate when the blades were locked into flight position. Vibration would cause a wire to break on one of these switches, opening the circuit, thereby indicating that the blades were still in the folded position. I sometimes think that Sikorsky put the AC inverters in the doghouse just so that we would have electrical power to repair these switches.”
During the FIP the Deuce pilots had carried out about 200 flight hours including instrument flying, single engine operations, and emergency procedures. The latter two, however, were not always scheduled. They also had hauled howitzers, jeeps and trucks, as well as external sling loads like fuel cells and concrete blocks up to 4,500 lb. When the FIP was completed in May 1957, the squadron pilots flew the green Deuces to New River, North Carolina, for full-scale squadron training.
Marine Deuces
The first operational Marine helicopter squadron using the HR2S, HMR(M)-461 (later redesignated HMH-461), was commissioned at the Marine Corps Air Facility, New River, North Carolina, on January 12, 1957. This new squadron was designed to support the operations of the Second Marine Division stationed at Camp Lejeune, N.C. but, according to Leahy, was like a continuance of the FIP for much of the first year. ”The Deuce didn't do much practical work because the Commanding Officer was an engineering zealot who just had to have everything perfect before he would commit the Deuce to duties as a prime mover”.
This attitude was replaced in spring of 1958 when Marine Air Group 26 (MAG-26) sent a detachment of HUS and HR2S helicopters on maneuvers aboard an aircraft carrier. Leahy adds, "The Deuces flew day and night, doing a whale of a lot of the 'dog work' in an amphibious landing." The Deuces proved themselves by having carried a huge tonnage of supplies and troops ashore during an operation known as PHIBEX 58, just off the coast of North Carolina. This operation finally proved their worth as a heavy transport helicopter.
Beside HMH-461, the only other operational Deuce squadron was HMH-462, stationed at the Marine Corps Air Station, Santa Ana, California. Originally the Marine Corps intended to have nine squadrons equipped with twenty HR2S helicopters each, but then chose the smaller but more reliable, single-engine Sikorsky HUS (S-58) as their standard transport. Therefore only 55 Deuces were delivered to the Marine Corps between July 1956 and February 1959. In September 1965, a detachment of eight Deuces were sent to Vietnam to support Marine Air Group 16 (MAG-16) at Marble Mountain in general transport duties. Although this detachment had only ten pilots for the eight aircraft, they flew about 5,400 hours in 1,500 missions and hauled more than 5,700 tons of cargo as well as some 31,000 passengers without an air accident.The Deuces in Vietnam saw their share of action and caught their share of enemy fire on supply runs up to the lip of the Demilitarized Zone, Dong Ha, and Con Thien. During Operation Hastings in autumn of 1966, one Deuce got 43 hits on a single mission, all from automatic weapons. Two of the Deuces carried 100,000 pounds of supplies during the Hastings mission alone. In early 1967, the first Sikorsky CH-53As arrived in Vietnam and the tough, noisy Deuces that had faithfully served the Marine Corps for ten years were shipped back to the states for storage.
Army Mojaves
The Army’s evaluation of the H-37 at Fort Rucker, Alabama included not only operational trials, but also maintenance and logistic activities. The results of the evaluation lead to an order of nine H-37A Mojave production versions in late 1954 which arrived at Fort Rucker during summer 1956.
The early Mojave version, not as complex as the Marines Deuce, had no automatic blade fold or pylon folding system, although it could be done manually, and also lacked the complicated ASE. Because of that, the Army Mojave was more reliable and easier to maintain than the Marine Deuce, but was limited to clear weather operations and was slightly harder to fly.The Mojave soon demonstrated what could be done with large transport helicopters when it lifted an M-56 tank with a 106 mm rifle weighing 5 tons at Fort Benning. The idea was that helicopter-borne tanks could quickly leap water, swamps or other areas that normally would present crossing problems.
In February 1958 Fort Benning also became home of the first operational Army Mojave unit, the 4th Helicopter Transportation Company. The 4th was also the first unit to take the Mojave overseas when it went to Germany in 1959 to support U.S. Forces in Europe. By May 1960, The Army received a total of 94 Mojaves and during the next two years returned 90 of them to Sikorsky where they were upgraded with reinforced retracting landing gear systems, crashworthy fuel tanks, and improved nose doors for unloading in hover. Also, the first Mojaves, lacking the ASE, were then equipped with a Lear Autostabilization System. All upgraded Mojaves were redesignated as H-37B and later as CH-37B.
Like the Marine Deuces, the Army Mojaves saw their share of action in Southeast Asia when a detachment of the 19th Transportation Company was sent to Vietnam to fulfil the heavy helicopter recovery role in 1963. By October 1964, nine Mojaves were in-country. The Mojaves demonstrated that they were capable of recovering intact aircraft up to the size of a Vertol H-21 with reduced disassembly time in hostile areas.
Nevertheless, maintenance personnel had always to work hard, usually under rough conditions in rice paddies or jungle clearings and often under fire, to remove rotor blades and engines from the crashed aircraft to prepare them for recovery. When the preparation work was done the Mojave came in and hovered over the downed aircraft while the crew hooked up the external sling under the watchful eyes of the Mojaves door gunners at their M60s. This was the most critical moment in a recovery operation since a low hovering Mojave naturally offered a rewarding target for enemy gunners.
At least one Mojave crashed, even without hostile activities, while attempting to sling-lift a downed UH-1B Huey from a clearing near Bien Hoa Airbase in September 1965. However, these dangerous jobs paid off. During summer and autumn of 1963, the first four Army Mojaves employed in Vietnam recovered downed aircraft with an estimated worth of more than 7.5 million U.S. Dollars.
That the Mojave did not see more extensive service in Vietnam is the result of its replacement in the Army inventory by more powerful turbine-driven helicopters like the CH-54 'Tarhe' and the CH-47 'Chinook' in the mid-sixties. In the late sixties all Mojaves were withdrawn from active Army service and handed over to Army National Guard units in Alabama, California, Iowa, Kansas and Texas where they still served until 1974.
Commercial service
In view of the accelerated interest in scheduled helicopter service by the airline industry, Sikorsky had endeavored to include in their developments the general requirements requested by commercial operators.
Regarding the H-37, sales representative R. B. Muir announced to the industry on January 19, 1954 that "The H-37 twin-engine transport development has received only limited publicity due to its classified nature, and we have been unable to determine just how soon general information can be released. However, it is a matter of public record that it is a single 5-bladed main rotor configuration, powered by two Pratt & Whitney R-2800 engines which will permit single engine operation over a major portion of its speed range". Muir asked the airline industry for indulgence and added that by late 1956 commercial modifications of the H-37 would be available, providing that the military planning is carried through. However, Sikorsky's hopes to sell the H-37 on the commercial market were never fulfilled. One major reason seemed to be the operating costs of these large piston-engine helicopters with their high consumption of expensive aviation gasoline. Future plans to modify existing H-37 helicopters with turbine engines for scheduled flights and other commercial activities were dropped in favor of newer turbine-driven helicopter designs.
Between 1971 and 1973 Keystone Helicopter Corporation of Philadelphia, PA, purchased all of the remaining H-37 helicopters in government storage. Keystone obtained FAA certification for these ex-military aircraft and successfully used a number of them commercially for external load construction work for several years. Stripped of all non-essential equipment, the FAA licensed H-37 was permitted to lift up to 10,000 pounds on the cargo hook. One typical working area of Keystone's former Deuces was the transportation and erection of wooden poles for power companies.
In late 1980, Keystone Aircraft reassembled and overhauled one of their stored H-37s, putting it into an airworthy condition again. This refurbished Deuce was painted in the colours of The U.S. Marine Corps and departed Tucson, Arizona, for it's final flight to the Naval Aviation Museum in Pensacola, Florida, on February 25, 1981.
Other H-37s can be found in The Army Aviation Museum at Fort Rucker, Alabama, The Army Transportation Museum at Fort Eustis, Virginia, and The Pima Air and Space Museum in Tucson, Arizona. The only European Museum owning an H-37/CH-37 is the International Helicopter Museum (IHM) in Weston-super-Mare, England. Unfortunately, the IHM’s CH-37 is still stored in the USA and due to its large size there is no feasible way of transporting it across the Atlantic at the moment.
adapted from Flugzug Classics article
When first publicly unveiled in January 1954, the Sikorsky H-37 was introduced by its manufacturer as a "giant, twin-engine transport” that represents a "tremendous advance in the art of designing and building helicopters".
In fact, the H-37 was the biggest, fastest and most powerful production helicopter in the free world until the introduction of Boeing Vertol's turbine-driven Chinook in 1961. Originally developed for the United States Marine Corps for transport of cargo and troops and for the evacuation of casualties, the H-37 had a gross weight of 31,000 pounds, more than four times that of its predecessor, the Sikorsky H-19 (S-55).
Short Development Period
After a relative short development period of only three years, the first H-37 prototype carried out its maiden flight with Sikorsky test pilot Jimmy Viner at the controls in Stratford, Connecticut, on December 12, 1953. A total of four pre-production versions, Serial No. 133732 to 133735, were built and underwent extensive evaluation under the military designation of XHR2S-1. Military production versions of the H-37 were designated by the Marine Corps as HR2S-1. The leading ‘X’ of the first four helicopters indicated that they were prototypes. Since the HR2S-1 was the second version of the transport helicopter, a ‘2’ was inserted in its name to indicate this. The Marines, being big on card playing and the ‘2’ card being called a ‘Deuce’, they nicknamed the HR2S-1 the ‘Deuce’.
The United States Army also noticed the potential of the H-37 and, in 1954, began to fly one of the four prototypes under the new designation YH-37. Later production versions were designated as H-37A. Following the Army's practice to name helicopters in honor of the American Indian tribes, they christened their H-37A the ‘Mojave’
Advanced design features...
The H-37, a very complex and advanced design helicopter, had incorporated into it many new features, such as 'clamshell' nose loading doors, similar to the Bristol 170 fixed-wing freighter, and a retractable main landing gear. It was also the first helicopter with a hydraulic main rotor blade fold system, automatic stabilization equipment (ASE), and the first twin-engine rotorcraft in U.S. military service. The airframe of the H-37 was an all-metal design consisting of the fuselage, main gearbox cowling, also referred to as the 'doghouse', stub-wings, engine nacelles, horizontal stabiliser and tail rotor pylon. The nacelles also accommodated the helicopter’s fully retractable main landing gear. The two-cell, 400-gallon capacity fuel tanks for each engine were located in the aft portion of the engine nacelles and in the adjacent stub-wing sections. This innovative arrangement made the 30-foot long cargo cabin clear for loading and unloading of troops or cargo up to a 105 mm howitzer and trailer. A cargo hatch, also referred as the ‘hellhole’, was located in the centre of the reinforced cabin floor and a cargo sling capable of carrying 10,000 pounds could be attached to hardpoints around the hellhole. In order to further assist in loading, an electric hoist, capable of lifting 2,000 pounds, was mounted on a monorail attached to the cabin ceiling.
...with Archaic engines
In contrast to its rather advanced design features, the H-37 was powered by archaic Pratt & Whitney Double Wasp R-2800 piston engines. It was used in many aircraft, including the famous Douglas DC-6 fixed-wing transport and even in World War II veterans like the Corsair and Thunderbolt.
The design of the H-37 helicopter called for the engines to be mounted in separate nacelles at the outboard end of each stub-wing, with driveshafts pointing inboard at an angle of approximately 80 degrees and upward at an angle of approximately 12.5 degrees. A hydro-mechanical clutch was splined to the output of each engine and a driveshaft connected the clutch to the main gearbox in the upper center of the fuselage. The main gearbox transferred power to the intermediate and tail rotor gearboxes and provided the correct gear reduction for the main and tail rotors.
There were two types of throttle controls in the pilot's compartment, the overhead throttle quadrant and a twist-grip throttle on each of the collective pitch controls. The quadrant throttles were used for engine starting, ground operation, clutch engagement and to synchronize the engines. Normally, during flight, the quadrant throttles were not used except for minor engine synchronization adjustments or for single-engine operation. The twist-grip throttle was used during flight and automatically synchronized the power setting of both engines whenever changes in the collective pitch occurred. The R-2800 radials powered the H-37 quite well and were very responsive to the throttles, but due to the inertia of this massive helicopter, pilots had to fly with much anticipation. It was said that maneuvers near the ground were indeed thrilling until the pilot mastered the twist grip throttle.
New World Records
In determining the maximum capabilities of the HR2S, the naval version of the H-37, two new weight lifting records and a new speed record were established at Bradley Field, Connecticut, between November 9 and 11, 1956. Piloted by Major Roy L. Anderson of the Patuxent River Naval Air Test Center and Sikorsky test pilot Robert Duke, the HR2S lifted a payload of six metric tons (13,260 pounds) to an altitude of 7,000 feet and a payload of five metric tons (11,050 pounds) to maximum altitude of 12,100 feet. The former weight record was 8,820 pounds at an altitude of 6,560 feet set in 1955 by a Russian Yakowlev Yak-24 tandem helicopter. Only one day after establishing the new records, Major Anderson reached a maximum speed of 162.743 miles per hour (142 knots) with an empty HR2S and set a new world speed record for helicopters. This topped the old speed record of 156.005 miles per hour (136 knots) set in 1954 by a turbine-driven Sikorsky XH-39 experimental helicopter.
Trials and troubles
The Marine Corps set great expectations on the brand new H-37 ‘Deuce’ which was designated as HR2S at that btime. In late 1956, Marine Corps Experimental Helicopter Squadron HMX-1, stationed at Quantico, Virginia, received its first two dark blue H-37 for squadron experimental evaluation. In the interim, new members of the Marine Medium Helicopter Squadron 461 HMH-461 attended ground school at the Sikorsky factory in Stratford Connecticut.
One of them, First Lieutenant Michael Leahy, now a retired Lieutenant Colonel, recalls, ”the first pilots came to Quantico in January of 1957 for the Fleet Introduction Program (FIP).” Awaiting them were four brand new green Deuces, serial numbers 140314 to 140318. In contrast to the already existing blue Deuces with serial numbers beginning with 138 and lacking dorsal fin at the base of the tail rotor pylon, the green Deuces were the full production configuration. The FIP was officially intended as a three-month evaluation of the HR2S helicopters under realistic conditions. According to Leahy, the squadron pilots, almost akin to test pilots, were to help weed out and correct discrepancies, which were certain to show up in the FIP. "For instance", he recalls, "there was a round main oil cooler in the original models of the Deuce, one in each engine pod. We found that they were not doing the job and the engines were overheating. Sikorsky replaced the offending coolers with more efficient square coolers which then became standard."
Another experience of Deuce pilot Leahy involved an engine clutch failure. As a senior First Lieutenant with a lot of helicopter time, compared to those who came to 461 immediately upon graduation from flight training at NAS Pensacola, he was flying with a new Second Lieutenant, doing touch-and-go landings. As they came to a hover just before touch down, the aircraft lurched rather violently down on the port side. The clutch on the port engine failed. Leahy recalls: ”I got the ship down okay, but noticed that the engine tachometer had pegged, indicating an overspeed. I quickly reached up for the offending throttle control lever on the overhead quadrant and gently pulled it back to idle. We then sat there until a crash truck arrived as a safety precaution.” A few of months earlier a Deuce burned up after a clutch failure at Quantico. ”In that instance, with a load on, the engine clutch assembly failed, causing the engine to overspeed”, recalls Leahy. ”The pilot yanked the throttle back post haste, causing a huge backfire and igniting fuel that was pouring from the punctured fuel cells, caused by flying debris from the cooling fan rotor buckets”.
Many problems of the Deuce were caused by vibration. Broken wires on the instrument panel were very common. John R. Tay, a former Deuce helicopter electrician, states that ”the biggest culprit was the automatic blade fold system. There was a switch on each blade that would indicate when the blades were locked into flight position. Vibration would cause a wire to break on one of these switches, opening the circuit, thereby indicating that the blades were still in the folded position. I sometimes think that Sikorsky put the AC inverters in the doghouse just so that we would have electrical power to repair these switches.”
During the FIP the Deuce pilots had carried out about 200 flight hours including instrument flying, single engine operations, and emergency procedures. The latter two, however, were not always scheduled. They also had hauled howitzers, jeeps and trucks, as well as external sling loads like fuel cells and concrete blocks up to 4,500 lb. When the FIP was completed in May 1957, the squadron pilots flew the green Deuces to New River, North Carolina, for full-scale squadron training.
Marine Deuces
The first operational Marine helicopter squadron using the HR2S, HMR(M)-461 (later redesignated HMH-461), was commissioned at the Marine Corps Air Facility, New River, North Carolina, on January 12, 1957. This new squadron was designed to support the operations of the Second Marine Division stationed at Camp Lejeune, N.C. but, according to Leahy, was like a continuance of the FIP for much of the first year. ”The Deuce didn't do much practical work because the Commanding Officer was an engineering zealot who just had to have everything perfect before he would commit the Deuce to duties as a prime mover”.
This attitude was replaced in spring of 1958 when Marine Air Group 26 (MAG-26) sent a detachment of HUS and HR2S helicopters on maneuvers aboard an aircraft carrier. Leahy adds, "The Deuces flew day and night, doing a whale of a lot of the 'dog work' in an amphibious landing." The Deuces proved themselves by having carried a huge tonnage of supplies and troops ashore during an operation known as PHIBEX 58, just off the coast of North Carolina. This operation finally proved their worth as a heavy transport helicopter.
Beside HMH-461, the only other operational Deuce squadron was HMH-462, stationed at the Marine Corps Air Station, Santa Ana, California. Originally the Marine Corps intended to have nine squadrons equipped with twenty HR2S helicopters each, but then chose the smaller but more reliable, single-engine Sikorsky HUS (S-58) as their standard transport. Therefore only 55 Deuces were delivered to the Marine Corps between July 1956 and February 1959. In September 1965, a detachment of eight Deuces were sent to Vietnam to support Marine Air Group 16 (MAG-16) at Marble Mountain in general transport duties. Although this detachment had only ten pilots for the eight aircraft, they flew about 5,400 hours in 1,500 missions and hauled more than 5,700 tons of cargo as well as some 31,000 passengers without an air accident.The Deuces in Vietnam saw their share of action and caught their share of enemy fire on supply runs up to the lip of the Demilitarized Zone, Dong Ha, and Con Thien. During Operation Hastings in autumn of 1966, one Deuce got 43 hits on a single mission, all from automatic weapons. Two of the Deuces carried 100,000 pounds of supplies during the Hastings mission alone. In early 1967, the first Sikorsky CH-53As arrived in Vietnam and the tough, noisy Deuces that had faithfully served the Marine Corps for ten years were shipped back to the states for storage.
Army Mojaves
The Army’s evaluation of the H-37 at Fort Rucker, Alabama included not only operational trials, but also maintenance and logistic activities. The results of the evaluation lead to an order of nine H-37A Mojave production versions in late 1954 which arrived at Fort Rucker during summer 1956.
The early Mojave version, not as complex as the Marines Deuce, had no automatic blade fold or pylon folding system, although it could be done manually, and also lacked the complicated ASE. Because of that, the Army Mojave was more reliable and easier to maintain than the Marine Deuce, but was limited to clear weather operations and was slightly harder to fly.The Mojave soon demonstrated what could be done with large transport helicopters when it lifted an M-56 tank with a 106 mm rifle weighing 5 tons at Fort Benning. The idea was that helicopter-borne tanks could quickly leap water, swamps or other areas that normally would present crossing problems.
In February 1958 Fort Benning also became home of the first operational Army Mojave unit, the 4th Helicopter Transportation Company. The 4th was also the first unit to take the Mojave overseas when it went to Germany in 1959 to support U.S. Forces in Europe. By May 1960, The Army received a total of 94 Mojaves and during the next two years returned 90 of them to Sikorsky where they were upgraded with reinforced retracting landing gear systems, crashworthy fuel tanks, and improved nose doors for unloading in hover. Also, the first Mojaves, lacking the ASE, were then equipped with a Lear Autostabilization System. All upgraded Mojaves were redesignated as H-37B and later as CH-37B.
Like the Marine Deuces, the Army Mojaves saw their share of action in Southeast Asia when a detachment of the 19th Transportation Company was sent to Vietnam to fulfil the heavy helicopter recovery role in 1963. By October 1964, nine Mojaves were in-country. The Mojaves demonstrated that they were capable of recovering intact aircraft up to the size of a Vertol H-21 with reduced disassembly time in hostile areas.
Nevertheless, maintenance personnel had always to work hard, usually under rough conditions in rice paddies or jungle clearings and often under fire, to remove rotor blades and engines from the crashed aircraft to prepare them for recovery. When the preparation work was done the Mojave came in and hovered over the downed aircraft while the crew hooked up the external sling under the watchful eyes of the Mojaves door gunners at their M60s. This was the most critical moment in a recovery operation since a low hovering Mojave naturally offered a rewarding target for enemy gunners.
At least one Mojave crashed, even without hostile activities, while attempting to sling-lift a downed UH-1B Huey from a clearing near Bien Hoa Airbase in September 1965. However, these dangerous jobs paid off. During summer and autumn of 1963, the first four Army Mojaves employed in Vietnam recovered downed aircraft with an estimated worth of more than 7.5 million U.S. Dollars.
That the Mojave did not see more extensive service in Vietnam is the result of its replacement in the Army inventory by more powerful turbine-driven helicopters like the CH-54 'Tarhe' and the CH-47 'Chinook' in the mid-sixties. In the late sixties all Mojaves were withdrawn from active Army service and handed over to Army National Guard units in Alabama, California, Iowa, Kansas and Texas where they still served until 1974.
Commercial service
In view of the accelerated interest in scheduled helicopter service by the airline industry, Sikorsky had endeavored to include in their developments the general requirements requested by commercial operators.
Regarding the H-37, sales representative R. B. Muir announced to the industry on January 19, 1954 that "The H-37 twin-engine transport development has received only limited publicity due to its classified nature, and we have been unable to determine just how soon general information can be released. However, it is a matter of public record that it is a single 5-bladed main rotor configuration, powered by two Pratt & Whitney R-2800 engines which will permit single engine operation over a major portion of its speed range". Muir asked the airline industry for indulgence and added that by late 1956 commercial modifications of the H-37 would be available, providing that the military planning is carried through. However, Sikorsky's hopes to sell the H-37 on the commercial market were never fulfilled. One major reason seemed to be the operating costs of these large piston-engine helicopters with their high consumption of expensive aviation gasoline. Future plans to modify existing H-37 helicopters with turbine engines for scheduled flights and other commercial activities were dropped in favor of newer turbine-driven helicopter designs.
Between 1971 and 1973 Keystone Helicopter Corporation of Philadelphia, PA, purchased all of the remaining H-37 helicopters in government storage. Keystone obtained FAA certification for these ex-military aircraft and successfully used a number of them commercially for external load construction work for several years. Stripped of all non-essential equipment, the FAA licensed H-37 was permitted to lift up to 10,000 pounds on the cargo hook. One typical working area of Keystone's former Deuces was the transportation and erection of wooden poles for power companies.
In late 1980, Keystone Aircraft reassembled and overhauled one of their stored H-37s, putting it into an airworthy condition again. This refurbished Deuce was painted in the colours of The U.S. Marine Corps and departed Tucson, Arizona, for it's final flight to the Naval Aviation Museum in Pensacola, Florida, on February 25, 1981.
Other H-37s can be found in The Army Aviation Museum at Fort Rucker, Alabama, The Army Transportation Museum at Fort Eustis, Virginia, and The Pima Air and Space Museum in Tucson, Arizona. The only European Museum owning an H-37/CH-37 is the International Helicopter Museum (IHM) in Weston-super-Mare, England. Unfortunately, the IHM’s CH-37 is still stored in the USA and due to its large size there is no feasible way of transporting it across the Atlantic at the moment.
adapted from Flugzug Classics article