Known by its military designation as the High Mobility Multi-purpose Wheeled Vehicle, the HMMWV is a lightweight, highly mobile, diesel-powered, four-wheel-drive tactical vehicle that uses a common chassis to carry a wide variety of military hardware ranging from machine guns to tube-launched, optically tracked, wire command-guided (TOW) anti-tank missile launchers. It must perform in a wide variety of terrain, from deserts to jungles, for long periods of time, with minimal maintenance. It has to carry its cargo and occupants in safety while dodging instruments of war — bullets, bombs and mines.
Its 15 configurations (cargo/troop carriers, weapons carriers, ambulances and shelter carriers) share a common engine, chassis and transmission, with 44 interchangeable parts that are used in more than one position. That means fewer training hours are necessary for the mechanics who will maintain it. Its simplified supply, maintenance and logistics system — essentially one set of common parts for 15 configurations — means lower life-cycle costs which saves tax dollars.
HMMWVs are maintainable, reliable and survivable. They meet all of these requirements while incorporating new standards of reliability for combat vehicles. They score high on Reliability, Availability, Maintainability and Durability (RAM-D) requirements and specifications. During initial production tests, the new vehicle proved to be nearly twice as durable as the Army required.
High ground clearance is a prerequisite for superior mobility. The 16-inch ground clearance of the HMMWV is an engineering feat considering that the vehicle stands only 72 inches high. Full-time four-wheel drive, independent suspension, steep approach and departure angles, 60 percent slope-climbing, 40 percent side slope and 60-inch water-fording capabilities combine with the high ground clearance to make the HMMWV an exceptional off-road vehicle.
The M998 A0 series has a curb weight of approximately 5,200 lbs., a payload of 2,500 lbs. (GVW 7,700 lbs.), and a 6.2 liter V-8 diesel engine with a three-speed automatic transmission. The current comparable model, the M1097A2, weighs only 700 lbs. more but can carry almost twice the payload at 4,400 lbs. (GVW 10,300 lbs). It has a 6.5-liter V-8 diesel with a four-speed automatic transmission. The current production Expanded Capacity Vehicle (ECV) model M1113 has a payload of 5,100 lbs. That is over 2 ½ tons, or very nearly the M1113's own weight of 6,400 lbs. The M1113 has a turbocharged 6.5-liter V-8 diesel. The up-armored variant M1114 is produced by AM General with the armor package installed by O'Gara Hess and Eisenhart.
As a centerpiece of the Army's vehicular force modernization, HMMWVs are air transportable and droppable, and can be sling-loaded by helicopters. Three HMMWVs can be carried in a C-130 Hercules transport aircraft and 15 in a C-5A Galaxy. In combat conditions, the HMMWV can be delivered by the Low Altitude Parachute Extraction System without the aircraft having to land.
The HMMWV has a low profile (six feet tall), a wide stance (seven feet wide) and is 15 feet long. These proportions contribute to a stable, road-hugging truck that is very difficult to roll over. This contrasts to the old M151 Jeeps that were considered unstable.
The HMMWV is constructed on a steel frame with boxed frame rails and five cross members constructed from high-grade alloy steel. Once the substructure is assembled, E-coating is applied to provide additional corrosion protection.
The aluminum body reduces weight and provides resistance to corrosion. Aluminum body panels are riveted and bonded together with technologically-advanced adhesives to provide additional strength. The body is designed to flex to accommodate off-road stresses.
The AM General-designed geared hub assembly in the power train doubles the torque to each wheel in the hub of the wheel. This also helps achieve 16 inches of ground clearance, far more than any other vehicle in its class. The use of a double A-arm independent suspension front and rear, coil springs and hydraulic double-acting shock absorbers gives the HMMWV unsurpassed mobility. Four-wheel disc brakes are mounted inboard against the sides of the differentials both of which are located up, between the frame rails, protecting them from impact and debris. Torque-biasing differentials allow the vehicle to continue to move forward as long as any one wheel has traction.
This unique configuration of components along with military 37 x 12.5 radial tires with low-profile runflat devices allows the HMMWV to go places that no other wheeled vehicle in U.S. or foreign military service could go. Some HMMWVs are equipped with an optional central tire inflation system (CTIS). This enables the operator to adjust tire pressure from the driver's seat "on the move" to adapt to changing terrain conditions for greater off-road mobility.
The M1097A2 series features a 6.5-liter Optimizer 6500 diesel engine built by AM General's subsidiary, General Engine Products. It is coupled to a four-speed automatic transmission and full-time four-wheel drive transfer case to provide the HMMWV with exceptional performance. (See specifications) The vehicle can reach speeds of more than 70 mph.
The truck utilizes a 12/24-volt electrical system and has a 25-gallon fuel tank. It has power-assisted hydraulic disc brakes and power steering.
The vehicle has either a 1 + 1 or 2 + 2 seating, depending on the model, on each side of the drivetrain, which is elevated, allowing the differentials to be raised. This, along with the geared hubs, contributes to high ground clearance. The location of the crew on each side of the drivetrain also allows for a low center of gravity.
The modular design of the HMMWV allows it to be easily re-configured for many different uses.