Virtual Museum of the Vietnam War

M274 "Mechanical mule" with 106mm recoilless rifle diorama

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History of development


The M274 vehicle was developed at the beginning of the fifties, to replace 1/4 ton (jeeps) and 3/4 ton (Dodge) class vehicles in infantry and airborne units. The new vehicle was intended to weigh less than 750 pounds (340,5 kg) and be able to carry 1000 pounds (454 kg) of cargo cross-country and a driver.

Prototype of the M247 was built by Willys and tested from 1953 to 1956. It was able to carry 850 pounds (386 kg) of cargo on improved roads. Two or four wheels were driven. It was possible to remove the driver's seat and to move the steering column to make more room for the cargo. Each wheel had a lifting eye, for sling-loading the vehicle under a helicopter, or for parachute drops. If the vehicle overturned while landing, it could be put by the soldiers "wheels down" and driven away again.

The new vehicle, called "mechanical mule" amazed with its versatility - apart from carrying personnel and supplies, it could be equipped with cable reels for setting up commo links, or armed, for example with a recoilless rifle, or with a guided anti-tank missile, and after wrapping with a tarp it could replace a raft for river crossing.

The M274 vehicles were built in following variants:

Total of 11 240 M274 family vehicles were built, including about 5 000 Mules that didn't return from Vietnam.

106mm Recoilless Rifle (M40)

The recoilless rifle is a kind of cross-over between a rocket launcher tube and a cannon. It is constructed so as to minimize the recoil by guiding a portion of the powder gasses to the rear of the weapon, thus compensating the recoil caused by the gasses pushing the projectile out of the tube. Unfortunately the gasses exiting to the rear of the recoilless rifle degrade the parameters of the weapon, and create a backblast which is potentially dangerous for the gun crew and also marks the position of the weapon by rising dust and debris. However the high mobility and flexibility of the weapon more than make up for the mentioned disadvantages.

The M40 recoilless rifle was developed in the early sixties as a result of experiences with unsuccessful M27 105 mm recoilless rifle. The M40 also has a calibre of 105 mm, but it is usually called 106 mm to indicate that the ammo for the M40 does not fit the M27. The M40 was designed primarily as an anti-tank weapon, the main types of ammo being the M334 HEAT (High Explosive Anti Tank) and the M346 HEP-T (High Explosive Plastic - Tracer) rounds. The HEAT rounds penetrates utilizing the Neuman/Munroe effect - shaped charge explosion forms a high-velocity jet of plasma that goes through the solid armor. The HEP rounds (also called squash head rounds) work differently, they don't actually go through armor plate - the charge of plastic explosive sticks to the target with a large contact surface and is then detonated, which induces a shock wave travelling through the armor plate, which in turn causes the fragmentation of armor plate as the wave exits. The resulting fragments demolish the inside of the armor plate. Because the powder gases guided to the rear of the recoilless rifle mark the position of the weapon very clearly, a hit with the first round is required. To achieve this, the optical sight of the recoilless rifle is backed up with a .50 caliber spotting rifle M8C, which "experimentally" verifies the aim without compromising tthe weapon's position. The spotting rifle uses a special 12,7x76 ammo, it's balistic parameters closely matching the 106 mm round.

In Vietnam the M40 recoilless rifle displayed it's flexibility - as there were no suitable targets for an anti-tank weapon, an APERS (anti personnel, also called bee-hive) round was designed, containing 6 000 steel flechettes (darts) for striking enemy soldiers. It was said this round converted the recoilless rifle in world's biggest shotgun.

A complete M40A1 system weights 485 pounds (220 kg), it's length is 11,2 feet (3 414 mm). Range is 8420 yards (7700 m) with muzzle velocity of 1650 fps (500 m/s).


The diorama depicts the M274A1 in the colours of the US Marines, carrying a 106 mm recoilless rifle (M40) in the suburbs of Hue, where, in the beginning of 1968, during the famous "Tet offensive" heavy street fighting occurred. There and under these circumstances, recoilless rifles mounted on light vehicles proved very valuable tool of urban warfare.

construction report

Specifications of the M274A1 vehicle

Length: 3004 mm
Height (at platform): 700 mm
Width: 1184 mm
Empty weight: 395 kg
Load capacity: 454 kg
Max range: 240 km
Max speed: 40 km/h
Propulsion: 4 cylinder, gasoline, air cooled, "boxer" engine, Willys AO4-53, 11,2 kW power
Transmission: Not syncronized gearbox, 3 speed forward plus reverse, 2 speed transfer case, permanent four wheel drive
Armament: M40 106 mm recoilless rifle with M8C spotting rifle



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