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 transfercase, 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 slingload 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.

The first Mechanical Mules, the M274 & M274A1, had a magnesium bed and axle housings with a four cylinder engine, four wheel drive and four wheel steering. The later M274A2, A3, & A4 had a magnesium beds and axle housings, four wheel drive, four wheel steering and a two cylinder engine. The last production model, the M274A5 has an aluminum bed and axle housings, with four wheel drive and two wheel steering. Optional A5 extras include electric starters, fording kits, wide wheels and fender kits. Mules will operate over all types of road, cross-country terrain, and in all types of weather and are capable of fording in up to 18 inches of water without modification. The Mule weighs only 860 pounds and its rated load is 1000 pounds. A spare wheel/tire is not included as the mule will operate on three wheel/tires.