Mack Defense's M917A3: A Commercial Workhorse Turned Military Mainstay
When the U.S. Army needed a new heavy dump truck to replace the aging AM General MM917 — a platform that had served for more than 40 years — it turned to an unlikely source: the commercial construction site.
The result is the Mack Defense M917A3 Heavy Dump Truck (HDT), a militarized derivative of the ubiquitous Mack Granite Class 8 chassis that has been hauling gravel, asphalt, and demolition material on civilian jobsites for decades. And the Army is clearly impressed. In March 2025, Mack Defense delivered its 500th M917A3 to the military, and just months later, a new five-year contract was signed for up to 450 more.
From Granite to Government Spec
The M917A3 is a textbook example of Heavy-Shift's core thesis — the convergence of commercial heavy technology and military application. Rather than designing a tactical truck from scratch, Mack Defense engineers started with the proven Mack Granite axle-forward chassis and ruggedized it for the battlefield.
Key modifications include heavier-duty rear axles, all-wheel drive (8×8 configuration), increased suspension ride height, and a Central Tire Inflation System (CTIS) for terrain adaptability. The result is a truck with a gross vehicle weight of 42.9 tonnes and a payload capacity of up to 27 tonnes — enough to haul heaped loads of rock, earth, and construction materials in the most austere environments.
Power comes from a Mack MP8 13-liter turbodiesel producing 440 hp and 1,660 lb-ft of torque, paired with an Allison 4500 Generation 5 six-speed automatic transmission. The cab is available in both standard and drop-in armored configurations, meeting U.S. Army blast requirements while maintaining the option to swap between mission profiles.
Production takes place at the Mack Experience Center in Allentown, Pennsylvania — a dedicated $6.5 million assembly line that has been operational since 2021 and leverages the workforce and supply chain from Mack's main plant in nearby Macungie.
A Renewed Vote of Confidence
The original 2018 contract authorized up to 683 trucks at a value of $296 million. To date, the U.S. Army, Army Reserve, and Army National Guard have ordered 549 trucks under that program. The new five-year contract, awarded June 24, 2025, extends production through 2030 with a ceiling of $221.8 million for up to 450 additional trucks. The first order under the new contract — 86 trucks — has already been placed.
"This contract represents continued confidence in our ability to deliver mission-critical vehicles to the U.S. Army," said David Hartzell, president of Mack Defense. The sentiment is echoed by the numbers: the M917A3 now handles military construction missions ranging from airfield and roadway building to disaster relief and supply depot maintenance.
Beyond the Dump Truck
The M917A3 is just one piece of Mack Defense's expanding military portfolio. Under the U.S. Army's Common Tactical Truck (CTT) program — which aims to replace roughly 35,000 heavy tactical trucks — Mack Defense delivered three prototypes to the Aberdeen Proving Ground in 2024. These include on-road and off-road tractors plus a load-handling system truck, all featuring high-voltage hybrid electric systems and architecture ready for autonomous integration. The program is expected to lead to a production contract valued at over $5 billion.
Separately, the U.S. Marine Corps awarded Mack Defense a 12-month development contract for its Medium Tactical Truck (MTT) program, which will eventually replace the MTVR fleet. The early requirement specifies three hybrid-electric cargo variants with 10-, 15-, and 20-foot beds, a 70% off-road / 30% on-road mission profile, and 60-inch water-fording capability. Mack Defense and competitor ND Defense (formerly Navistar) each received Phase II prototype contracts in early 2025.
The Bigger Picture
Mack Defense's success with the M917A3 comes against the backdrop of a massive U.S. military investment in tactical wheeled vehicles. Oshkosh Defense secured a $1.54 billion follow-on contract for the Family of Heavy Tactical Vehicles (FHTV V) program in 2024, ensuring production of heavy tractors, load-handling systems, and trailers through 2031. With over 71,000 modernized heavy tactical vehicles delivered to date, Oshkosh remains the heavyweight — but Mack Defense is rapidly carving out its niche.
The message from the Army is clear: proven commercial platforms, militarized to spec and backed by robust supply chains, offer a faster, lower-risk path to fleet modernization than purpose-built designs. For a company that has supplied the U.S. military since World War I, Mack Defense's bulldog is proving it still has plenty of bite.
