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.
The M274 is officially known as the Army Mule or Mechanical Mule. It was developed out of a requirement for an infantry ammunition, light cargo, personnel, and weapons carrier. It was adopted for service in 1957 and used with the US Army, Marine Corps, and to limited extent with the Navy, Seabees and Air Force. The first models, the M274 and the M274A1, had a four cylinder horizontally opposed, air cooled Willys engines.The later models, the M274A2, M274A3, M274A4, and M274A5 have a two cylinder, horizontally opposed air cooled military standard engine. The M274A5 has an aluminum platform while the other versions are constructed of magnesium alloy.
The M274 consists of a platform mounted on two drop axles with four wheels. The engine is rear mounted. It has no suspension system other than low pressure tires. All models are equipped with full time four-time four wheel drive, two speed transfer case, and a three forward and one reverse speed transmission. A quick change mechanism allows for either two- or four-wheel steering on the M274, A1, A2, A3, and A4 models. The mule is equipped with a cargo retaining set of rails can be raised to accommodate the payload or lowered for shipping, storage, or flat bed operations. The seat (which can be adjusted to two positions on all models except the M274 and A3) and the foot rest can be detached and stowed underneath the platform for air transport. The driver can extend the steering column brace forward to allow operation while walking or crouching in front of the vehicle. The M274A1/A2/A3/A4/A5 are equipped for sling load operations. It is designed to carry a maximum of one thousand pounds of cargo over most types of terrain, but has no published towing capability as no hitch is installed. All models of the M274 may be turned on their sides or top to ease maintenance, repair, or lubrication operations.
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:
M274 - produced by Willys 1956 - 1960, 2 452 built. Four wheels steer, four cylinder gasoline "boxer" engine AO4-53.
M274A1 - produced by Willys 1962 - 1964, 1 905 built. Four wheels steer, four cylinder gasoline "boxer" engine AO4-53, weapons carrier variant.
M274A2 - produced by Bowen McLaughlin/York (BMY) 1964 -1967, 3609 built. Four wheels steer, two cylinder gasoline "boxer" engine AO-42.
M274A3 - M274 with its engine replaced by AO-42
M274A4 - M274A1 with its engine replaced by AO-42
M274A5 - produced by Baifield Industries 1965 - 1969, 2400 built and by Bruswick Corp. 1968 - 1970, 874 built. Only front wheels steer, two cylinder gasoline "boxer" engine AO-42.
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 back blast 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 caliber 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 traveling 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 the weapon's position. The spotting rifle uses a special 12,7x76 ammo, it's ballistic 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).