The HEMTT (Heavy Expanded Mobility Tactical Truck) is an eight-wheeled diesel-powered tactical truck with a weight rating of 9,100 kg. The M977 HEMTT entered service with the U.S. Army in 1982 as a replacement for the M520 Goer, and has continued to be produced for the U.S. Army and other countries ever since. By the second quarter of 2021, Oshkosh Defense has produced approximately 35800 HEMTTs in various configurations under new production contracts, and approximately 14,000 have been upgraded.
The HEMTT is designed to supply and resupply combat vehicles and weapon systems. The HEMTT is available in a variety of configurations, including truck, tanker, tractor and tow truck. The HEMTT was designed from the outset as a tactical truck, but to minimize procurement and life cycle costs, it incorporated paramilitary commercial vehicle components, including engine and transmission, whenever possible. On all HEMTT variants, the chassis is constructed of heat-treated carbon-manganese steel with a yield strength of 758 MPa.
The HEMTT’s two-door front control cab seats two people. It is a heavy-duty welded steel structure with corrosion-resistant sheet metal cladding. This cab meets the U.S. Army’s Long Term Armor Strategy (LTAS) requirements under the A- and B-kit armor philosophy. It also comes standard with integrated floor armor, an integrated machine gun mount with gunner protection kit, and air conditioning.
A Detroit Diesel 8V92TA V-8 two-stroke diesel engine rated at 445 hp (332 kW) is installed in the HEMTT A0 and HEMTT A1 models, and a DDECIV version of this engine is installed in the HEMTT A2. The HEMTT A4 models are equipped with a six-cylinder, 15.2-liter EPA 2004-compliant Caterpillar (CAT) C-15 diesel engine developing a peak output of 515 hp (384 kW). HEMTT A0 and A1 models are equipped with an Allison HT 740D 4F / 1R automatic transmission, torque converter and 55,000 lb (25,000 kg) Oshkosh two-speed transfer case. HEMTT A2 models are equipped with an Allison HD 4560P 6F/1R automatic transmission. HEMTT A4 models are equipped with an Allison 4500SP 5F / 1R automatic transmission and a 25,000 lb (25,000 kg) reinforced version of the Oshkosh two-speed transfer case.
The front axles on all HEMTTs are Oshkosh 46K single-stage axles, while the rear axles are Dana single-stage axles, which vary depending on configuration. Drive to the front axles is disconnectable. All axles have differential lock. Suspension on A0/A1/A3 models is on Hendrickson leaf springs with balancing beams. Suspension on A4 models is Holland air suspension, rear axle capacity depends on configuration. Tire size is 1600 R20 on all models, with Michelin XZL tires standard.
All models are capable of traversing water obstacles up to 1.2 meters deep and traversing a slope of at least 60%. All initial variants can be airlifted on the C-130. All variants can be airlifted on a C-17. The original HEMTT models have an A0 suffix. Only the M984 tow vehicle was produced in the A1 configuration. All models were produced in the A2 configuration. The A3 suffix applies to HEMTT demonstration models with a diesel-electric drive system. Current production HEMTT models have the suffix A4.