Virtual Museum of the Vietnam War

M55 Quad 50 Emplacement Diorama

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History of development

In the beginning of nineteen hundred forties the U.S. coastal artillery decided the idea of mounting anti-aircraft machine guns on trucks worth considering. Consequently a request was sent to several manufacturers, including W.L. Maxson, to develop an electrically driven mount for two .50 (12,7 mm) Browning M2HB machine guns for anti-aircraft use. The Maxson mount successfully passed the trials, entered production in 1942 and was used to equip the M13 half-track anti aircraft vehicle. In April 1942 the U.S. Army, encouraged by the M13's success asked the Maxson company to start working on a new mount, holding four machine guns. The requested mount was created using parts of the previous design and was designated M45 by the U.S. Army. The M45 mount equipped M16 vehicles entered production in May 1943. There were also slightly different M17 vehicles, manufactured mainly for the purposes of the Lend-Lease program and sent to Soviet Union and Great Britain. The M45 mount was also installed on a twin-axle M51 trailer, meant to be towed behind a 2,5 ton truck. The usability of this trailer encouraged the design of a lighter trailer for airborne units. This light, single axle trailer was named M55 and could even be towed behind a jeep. It was the M55 trailer that remained in service the longest of all designs described above.

The quad M2 machine gun on a M45 mount was a very potent weapon. In WWII it was successfully employed to fight against low-flying enemy aircraft. As the allies gathered air superiority, new job was found for the "unemployed" anti-aircraft vehicles - it turned out they were well suited to fight against ground targets. Their efficiency prompted their users to call the quad 50s "meat grinders". Sometimes a unit harassed by enemy sniper would call for M16 support, to which the general direction of the enemy was pointed out, and it's quad 50 would literally mow down trees, in which the sniper was hiding, thus eliminating the threat. It's worth mentioning, that the international law permits the use of automatic weapons above 11mm caliber against people only in self defense.

The M45 mounts were widely and successfully used in Korean War, mainly to fight against ground targets. Then the M16 vehicles were withdrawn from use and only the M55 trailers remained in the inventory of the U.S. Army. They were supposed to operate together with a truck, that carried ammunition for the quad, and on which the trailer was loaded for transport. This way the wear of the trailer could be reduced, and the mobility and flexibility of the system was increased. The quad could also shoot without dismounting it from the truck.

In the middle of nineteen hundred sixties the U.S. Armed Forces were engaged in the Vietnam War. Air Defense Artillery units, also M55 equipped, were sent to Republic of Vietnam as part of the American war effort. Lack of North Vietnamese air threats once again led to using the anti-aircraft weapons against ground targets. The Quad Fifties were mainly used to secure perimeters of forward area bases and also, mounted on trucks to provide convoy security. A helicopter was often used to move the quad to its firing emplacement. There was also at least one case of emplacing the quad on a barge to fire at targets located on the river banks. The quad was usually a prime target for the enemy and soldier serving nearby considered them "mortar magnets" and preferred maintaining some distance between them and the quad.

The M55 was equipped with three jacks, on which it could be lifted, and then, after removing the wheels, the base was lowered on the ground, providing good support for its weapons. For transport the M55 was lifted using its jacks, which enabled putting the wheels back on the trailer.

The M55, which were aging quickly, were withdrawn from U.S. Army's inventory shortly after American withdrawal from Vietnam.


The featured diorama shows the M55 trailer emplaced for firing on top of an old french bunker, many of which were built throughout all of Vietnam, near the town of Dong Ha. The crew of the quad is nearby - the crew chief, the gunner and two ammo loaders. Any second the enemy can start shooting at the base and then the quad will have to spring into action and return fire.

construction report

Specifications of M55

Length: 2889 mm
Height (for transport): 1607 mm
Height (for firing): 1429 mm
Width (for transport): 2092 mm
Width (for firing): 1397 mm
Empty weight: 1340 kg
Ground clearance: 178 mm
Armament: Four heavy 12,7 mm (.50) M2HB machine guns, with electrical firing mechanism
Rate of fire: 2200 rounds per minute
Traverse: 360 degrees
Elevation: -10 degrees to 90 degrees
Angular velocity of traverse and/or elevation: 60 degrees per second
Towing speed on road: 16 km/h
Towing speed off road: 8 km/h
Fording: 0,46 m
Crew: 4 people


Technical Manual 9-2010 Multiple Cal. .50 Machine Gun Mounts M45, M45C, M45D, and M45F; Multiple Cal. .50 Machine Gun Trailer Mount; and Mount Trailer M20 (PDF format - Adobe Acrobat Reader required)


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