The Heavy Expanded Mobility Tactical Truck, known universally as the HEMTT, is an eight-wheeled giant that has served as the backbone of American military logistics for over four decades. With its distinctive cab-forward design and massive cargo capacity, the HEMTT can haul 10 tons of supplies across terrain that would defeat most commercial trucks. For anyone interested in military vehicles, the HEMTT represents the evolution of heavy tactical transport from basic cargo trucks to sophisticated logistical systems.
Development History
The HEMTT program began in the late 1970s when the Army recognized its existing heavy trucks were reaching the end of their useful lives. The M520 Goer and M125 series vehicles had served well, but they couldn’t meet the demands of modern mechanized warfare. The Army needed a truck that could keep pace with armored units, carry more cargo, and operate reliably in harsh environments.
Oshkosh Corporation won the competitive contract in 1981, beating out established truck manufacturers with an innovative design that prioritized mobility over all else. The first HEMTTs rolled off the production line in 1982, and the Army immediately recognized they had something special. Initial orders expanded rapidly as commanders saw what the new trucks could accomplish.
The design philosophy behind the HEMTT emphasized commonality—all variants share the same engine, transmission, axles, and cab. This approach dramatically simplified maintenance and parts supply. A mechanic trained on one HEMTT variant can work on any other, and parts from one truck can be swapped into another regardless of its specific configuration.
Technical Specifications
Understanding the HEMTT’s capabilities starts with its impressive specifications:
- Configuration: 8×8 (all-wheel drive)
- Engine: Detroit Diesel 8V92TA, 445-500 horsepower depending on variant
- Transmission: Allison CLT-754 or CLT-755 automatic, 5 forward speeds
- Payload Capacity: 22,000 pounds (11 tons) typical, varies by variant
- Gross Vehicle Weight: 66,000 pounds maximum
- Maximum Speed: 57 mph on improved roads
- Range: 300+ miles depending on terrain and load
- Fording Depth: 48 inches without preparation
- Grade Climbing: 60% gradient
The 8×8 drivetrain gives the HEMTT exceptional off-road mobility. Each axle can articulate independently, allowing the wheels to maintain contact with uneven terrain. The Central Tire Inflation System (CTIS) lets the driver adjust tire pressure on the fly—lowering pressure for soft sand or mud, raising it for improved roads. This system alone dramatically extends the HEMTT’s operational envelope.
Major Variants
The HEMTT family includes numerous variants, each optimized for specific missions. Understanding these variants reveals the flexibility built into the original design.
M977 Cargo Truck
The baseline HEMTT cargo truck features a 20-foot cargo bed capable of carrying 10 tons of supplies. A materials handling crane mounted behind the cab can load and unload pallets without external support. This variant forms the backbone of combat support units, hauling everything from ammunition to spare parts.
M978 Fuel Tanker
Arguably the most critical HEMTT variant, the M978 carries 2,500 gallons of fuel for aircraft and ground vehicles. During Operation Desert Storm, M978s kept the armored advance moving by rushing fuel forward to thirsty tanks and Bradley fighting vehicles. The tanker can refuel multiple vehicles simultaneously using its multiple dispensing stations.
M983 Tractor
The M983 trades its cargo bed for a fifth wheel coupling, allowing it to pull heavy trailers. Its most famous role is hauling Patriot missile launchers and the M270 Multiple Launch Rocket System (MLRS). The M983’s ability to position these systems quickly gives air defense and artillery units unprecedented mobility.
M984 Wrecker
When heavy vehicles break down or get stuck, the M984 wrecker responds. Its massive crane can lift entire wheeled vehicles or heavy components from disabled trucks. The winches can pull stuck vehicles from mud, sand, or snow. Recovery units equipped with M984s can keep logistics convoys moving despite mechanical failures or terrain challenges.
M985 Cargo with Crane
Similar to the M977 but with a more powerful materials handling crane, the M985 specializes in loading and unloading heavy individual items. Ammunition supply units favor this variant because the crane can handle individual pallets of artillery rounds precisely.
M1120 Load Handling System
The most recent major variant adds a hook-arm load handling system similar to the PLS. This allows the HEMTT to rapidly exchange flatracks loaded with standardized cargo. Units can pre-position loaded flatracks at supply points, dramatically reducing turnaround time for delivery trucks.
The A4 Upgrade Program
Beginning in 2006, Oshkosh introduced the HEMTT A4 upgrade package to modernize aging vehicles. The A4 program replaced the Detroit Diesel engine with a more powerful and fuel-efficient Caterpillar C15, upgraded the transmission to a six-speed Allison 4500SP, and added an anti-lock braking system.
The A4 trucks also received improved armor protection designed for the insurgency threats encountered in Iraq and Afghanistan. Additional armor around the cab, blast-resistant seats, and run-flat tire inserts gave crews better chances of surviving improvised explosive devices (IEDs).
Perhaps most importantly, the A4 upgrade extended the HEMTT’s service life by decades. Trucks originally built in the 1980s could be rebuilt to A4 standards, combining new components with proven chassis and running gear. This approach saved money while maintaining operational readiness.
Combat History
The HEMTT has supported every major American military operation since its introduction. In Operation Desert Shield/Desert Storm, HEMTTs moved the mountains of supplies needed to sustain half a million troops in the Saudi desert. M978 fuel tankers were particularly critical, keeping the hundred-hour ground war’s armored advance fueled.
In the Balkans during the 1990s, HEMTTs operated over narrow mountain roads and through villages that challenged even experienced drivers. The trucks’ maneuverability surprised observers who expected eight-wheeled giants to be clumsy in confined spaces.
Operations Iraqi Freedom and Enduring Freedom tested the HEMTT as never before. Convoys faced ambushes, IEDs, and small arms fire regularly. The trucks’ size actually provided some protection—the driver and passenger sat high above the typical IED blast zone. Add-on armor kits improved survivability further, though they reduced payload capacity and increased fuel consumption.
Drivers learned to push the vehicles hard during convoy operations, maintaining speed to reduce exposure to ambush sites. The HEMTT’s highway speed of 57 mph, once considered adequate, became critically important when seconds meant the difference between life and death.
International Operators
While the United States operates the largest HEMTT fleet, several allied nations have adopted the vehicle. The United Kingdom evaluated HEMTTs before selecting an alternative, but maintained interest in the platform. Other NATO allies and Middle Eastern partners operate smaller HEMTT fleets purchased through Foreign Military Sales.
Australia operates a significant HEMTT fleet as part of their military logistics system. The vehicles’ proven reliability and parts availability through U.S. supply channels made them an attractive option for the Australian Defence Force.
Civilian Applications
Surplus HEMTTs regularly appear in the civilian market, where their capabilities find various applications:
Firefighting: Some fire departments and wildland firefighting agencies use former M978 tankers as water carriers. The all-wheel-drive system allows them to reach remote fire lines inaccessible to conventional fire trucks.
Oil and Gas: Energy companies operating in remote locations appreciate the HEMTT’s ability to deliver heavy equipment over unimproved roads. The cargo variants can haul drilling supplies where commercial trucks can’t reach.
Heavy Haul: The M983 tractor variant, with its heavy fifth wheel, can pull oversize loads that exceed standard tractor-trailer ratings. Specialized transport companies use them for moving construction equipment and industrial machinery.
Collections: Military vehicle enthusiasts prize the HEMTT for its impressive size and capability. Restored examples appear at shows and events, demonstrating the vehicle’s mobility and power.
Buying a Surplus HEMTT
For those considering HEMTT ownership, several factors deserve careful consideration:
Acquisition Cost: Surplus HEMTTs typically sell for $20,000 to $75,000 depending on variant, mileage, and condition. Wreckers and specialized variants command premium prices due to their utility.
Operating Costs: Fuel consumption runs 3-5 miles per gallon. The Detroit Diesel engines are thirsty but reliable, provided they receive proper maintenance. Insurance and registration for vehicles this size can be complex.
Maintenance: The common components shared across HEMTT variants mean parts are relatively available through military surplus channels. Oshkosh maintains support for civilian operators, though response times vary. The Allison transmission and Detroit Diesel engine use some commercial components that eases parts sourcing.
Licensing: Operating a HEMTT requires a Commercial Driver’s License (CDL) with appropriate endorsements. The vehicle’s weight and air brakes trigger CDL requirements in all U.S. states.
Storage: At over 33 feet long and nearly 10 feet wide, the HEMTT requires substantial storage space. Most residential garages cannot accommodate these vehicles.
The HEMTT’s Future
The Army continues modernizing its HEMTT fleet while developing next-generation replacements. The Common Tactical Truck program aims to eventually replace aging HEMTTs with newer designs, but budget constraints and the vehicles’ continued effectiveness have extended the timeline.
Meanwhile, Oshkosh continues winning contracts for HEMTT production and upgrades. The company’s investment in the platform ensures parts availability and technical support for decades to come. Current projections suggest HEMTTs will remain in U.S. military service through at least 2040.
Conclusion
The HEMTT represents American military engineering at its most practical. Rather than pursuing exotic technology, Oshkosh designed a truck that does its job reliably, day after day, in the harshest conditions imaginable. Its 8×8 drivetrain, powerful engine, and versatile variants combine to create a logistics vehicle that has supported American forces through four decades of operations worldwide.
For military vehicle enthusiasts, the HEMTT offers an accessible example of heavy tactical transport. Surplus vehicles are available, parts exist, and the trucks themselves demonstrate capabilities far beyond civilian counterparts. Whether you’re studying military logistics or considering purchasing a piece of military history, the HEMTT deserves attention as one of the most important tactical trucks ever built.
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