Gama Goat

The Gama Goat is a six-wheel drive semi-amphibious off-road vehicle originally developed for use by the US military in the Vietnam War. The Goat uses an articulated chassis, so that from distance it appears to be a four-wheel drive vehicle pulling a two-wheel trailer, but it is a single six-wheel vehicle with a four-wheel steering arrangement with the front and rear wheels turning in opposite directions. It was famous for its ability to travel over exceptionally rough and muddy terrain.

M561 Gama Goat
M561 "Gama Goat"
Type6×6 Cargo
Place of originUnited States
Service history
In service1970s–1990s
Used byUnited States and Mexico
Production history
DesignerChance-Vought Aircraft
Designed1962–1966
ManufacturerCONDEC
Unit cost$13,281[1]
Produced1969–1973
No. built14,274
VariantsM792 Ambulance
Specifications
Mass7,275 lb (3,300 kg)
Length227 in (5.8 m)
Width84 in (2.1 m)
Height91 in (2.3 m)
Crew1
EngineDetroit Diesel 3-53
160 cu in (2.6 L) Diesel I3
101 hp (75 kW), 217 lbf⋅ft (294 N⋅m)
SuspensionWheel 6×6
Operational
range
420 mi (680 km)
Maximum speed 56 mph (90 km/h)

The vehicle's nickname came from two sources: "Gama" from the name of the inventor of its powered articulated joint, Roger Gamaunt, and "Goat" for its mountain goat-like off-road ability. Its military designation was M561, 6×6 tactical 1¼-ton truck. There was also an ambulance version known as the M792. The vehicle was replaced by a variety of Commercial Utility Cargo Vehicles (CUCV) and Humvees (HMMWV)

History

The concept for the vehicle came when the French Army reported that the United States Army trucks provided to them were woefully inadequate for the terrain in Vietnam. In 1959, ARPA (now known as DARPA) funded a research project called Project "Agile" to develop a new tactical truck for the Southeast Asia theatre, as well as other projects of interest to the then-looming Vietnam War.

Of 50 companies solicited for XM561 proposals, six entered the competition,[2] including Clark, General Motors and LeTourneau Technologies, but on 15 March 1963, the research & development contract was awarded to Chance Vought division of LTV Aerospace, Dallas, Texas,[3] best known for their combat aircraft (though, actually the company did have some experience in designing ground vehicles, particularly, a predecessor of Gama Goat, but they didn't have the truck assembly lines and production experience comparable to those of the mentioned car manufacturers).[1] The principal competitor to the Goat was a tracked XM571 Articulated Utility Carrier developed by Canadair Ltd. of Montreal (yet another aerospace company,) which eventually lost the contest. The research and development contract for the Goat was completed by LTV at cost of about $8.7 million, over three times more expensive than when it had been awarded.[3]

The vehicle weighed almost three times as much as originally requested by the military and specified by the operational requirements (2,500 lbs). Field testing had not been completed before the mass production order had been issued. During the field tests, it had not been able to go 20,000 miles without a breakdown.[4]

Final construction of the vehicles was conducted by the Consolidated Diesel Electric Company (CONDEC) at their factory in Charlotte, North Carolina (on 11 June 1968, the Army awarded them a 3-year contract for 15,274 vehicles, 13,516 Army and 1,758 Marine Corps, at a total price of about $132.1 million, on the same day Detroit Diesel Division of General Motors received $30 million 3-year contract for the engines).[3] CONDEC also had factories in Schenectady, New York, where the Gama Goat was originally manufactured, and in Greenwich, Connecticut, where the parts for the Gama Goat were produced. In the early 1960s, the company moved to Waterbury, Connecticut for a few years, then closed their plants in New York and Connecticut to move to Charlotte, North Carolina for cheaper labor and facilities.

The Gama Goat was replaced in the late 1980s by a variety of CUCVs[5] and "Humvees" (HMMWV).[6]

Description
Gama Goat ride at the Muckleburgh Collection

Overall, some 14,274 Gama Goats were built at a cost of US$8,000 each (1965 dollars; equivalent to $64,904 in 2019); this was considered quite high at the time. 12,516 were slated for the US Army and 1,758 for the USMC. While the Gama Goat had exceptional off-road ability, its quirky steering made it hard to handle on pavement, and its tendency to flounder in amphibious operations required drivers to have special training in order to operate it. This meant that it could not be the "general purpose" vehicle the Army had hoped for, and production was halted after the original contract expired.

The air-cooled engine used in the original prototypes overheated in use, and was replaced in the production vehicles with a liquid-cooled Detroit 3-53 Diesel engine. Due to the high-intensity noise from the two-stroke Diesel engine, the drivers required hearing protection. The double hull construction and complex articulated drivetrain made maintenance difficult (the lubrication order alone took around six hours). In service in Vietnam, Gama Goats would often be sent out ahead of other vehicles in order to arrive at their destination at the same time.

While technically listed as amphibious, the Gama Goat's swimming capability was limited to smooth water crossings of ponds, canals and streams due to the very low freeboard and the lack of a propeller. Propulsion in the water was supplied by the six spinning wheels, and bilge pumps were standard equipment. Drivers had to remember to close the hull's drain openings before swimming the vehicles. Some models had extra equipment installed that made them too heavy to swim, such as heavy-duty winches, communications shelters that made them top heavy, or radar gear.

It was designed to be air-transportable and droppable by parachute.

Typical problems and malfunctions

In May 1972 Fort Hood cited the following problems as a result of examining 566 vehicles:

Typical problems chart[7]
Problem areaNumber
of vehicles
with faults
Defective brake drums, seals, “O” rings23
Water in differentials35
Wheel brake cylinder leaking41
Defective signal lights20
Gear box low on oil354
Transmission leaking at dowel pins top cover19
Loose wheel bearings356
Transfer case oil pump inoperable (no prime—some with Teflon tape in ball checks)188
Transfer case jumps out of high range (improper manufacture of main shaft splines)10
Vent pipe missing on rear differential11
Defective seat, tube, spindle assembly (brass brake line seat)42
Hood hinge broken10

Additional specifications

Articulation
  • Roll at center axle: ± 15 degrees
  • Roll at rear axle: ± 30 degrees
  • Pitch at rear axle: ± 40 degrees
  • Wall climb (vertical): 18 in (460 mm)
  • Angle of approach: 62 degrees
  • Angle of departure: 45 degrees
  • Hump angle: 140 degrees

Suspension
  • Front and rear independent coil springs at each wheel
  • Center single leaf spring and swing axle

Steering system
  • Type: Mechanical front and rear simultaneously operated
  • Steering ratio: 24:1
  • Turning radius: 29 ft (8.8 m)

Variants
  • M561
  • Cargo / personnel (eight troops) carrier
  • TOW ATGM team carrier (originally intended to be a dedicated Anti-Tank variant with its own TOW launching platform)
  • Communications (separate shelter installed in the cargo compartment)
  • Mortar carrier
  • Radar (counter-mortar/artillery system)
  • Radar (FAAR System)
  • M60 Machine gun and mount on passenger fender
  • M792
  • Ambulance
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See also
  • G-numbers
  • List of "M" series military vehicles

References
  1. Statement of Dr. J. Ronald Fox, Assistant Secretary of the Army, The Acquisition of Weapons Systems, May 21, 1970, pt. 2, p. 470.
  2. Contractor Selected for Missile B & XM561 Truck. // Army Research and Development, November 1962, v. 3, no. 11, p. 25.
  3. Gama Goat Contract Data by R.F. Keller, Assistant Comptroller General of the United States, Washington, D.C., 6 October 1970, p. 487.
  4. Statement of Hassell B. Bell, Associate Director, Defense Division, Office of the Comptroller General of the United States, 20 May 1970, pp. 394-395.
  5. "Dodge and Chevrolet CUCV". olive-drab.com. 7 July 2012. Retrieved 18 October 2016.
  6. Turnbull, Grant (30 September 2014). "End of an icon: the rise and fall of the Humvee". army-technology.com. Retrieved 18 October 2016.
  7. Army Procurement of the M561, Gama Goat, July 25, 1972, U.S. GPO, p. 17.
  • SNL G874
  • Doyle, David (2003). Standard Catalog of U.S. Military Vehicles. Kraus Publications. pp. 102–104. ISBN 0-87349-508-X.
  • Ware, Pat (2010). The World Encyclopedia of Military Vehicles. Lorenz Books. p. 228. ISBN 978-0-7548-2052-9.
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