This is a 1990 BMY M931A2 6×6, it’s an ex-U.S. military truck that was professionally converted into an expedition camper by Plan B Trucks of Utah.
Inside, the camper has wood-paneled walls and flooring, a dinette, fold-down sofa, multiple sleeping areas, a full galley with induction cooktop, microwave and refrigerator/freezer, plus separate wet and dry bathroom areas. It also includes extensive storage, a swing-out TV, LED lighting, diesel heating, air conditioning, and a lithium/solar-powered house electrical system.
Fast Facts: A BMY M931A2 6×6 Overlander
- This 1990 BMY M931A2 6×6 began life as a U.S. military 5-ton hauler before Plan B Trucks of Utah converted it into an expedition camper in 2017. The finished vehicle measures 36 feet long and keeps its heavy-duty military chassis, drivetrain, air brakes, and central tire inflation system.
- Power comes from an 8.3 liter Cummins 6CTA turbodiesel inline-six producing 240 bhp and 745 lb ft of torque, paired with an Allison 5-speed automatic and dual-range transfer case. The truck also keeps its Rockwell axles, while twin 75-gallon diesel tanks provide substantial range for long-distance travel. Although, with current fuel prices, a fill up will bring a tear to your eye.
- The purpose-built camper has wood-paneled walls and flooring, a dinette, fold-down sofa, multiple sleeping areas, full galley, refrigerator/freezer, induction cooking, wet and dry bathroom areas, diesel heating, and air conditioning. Nine solar panels, lithium batteries, an inverter, shore power, and substantial water storage are all included for extended off-grid use.
- The completed vehicle appeared on the television series “Extreme RVs” in 2017, which features unconventional and large-scale motorhomes. It has reportedly covered about 22,000 miles, received new 395/85R20 Goodyear tires in 2026, and is now being offered for sale from Golden, Colorado with supporting build documentation.
History Speedrun: The BMY M931A2 6×6
The M931A2 was the tractor-truck version of the M939A2, the turbocharged generation of the U.S. Army’s M939 series of 5-ton 6×6 trucks. The model names/numbers aren’t easy to remember, but they didn’t need to be, they were targeted squarely at military buyers and not your everyday consumers.
This 1990 BMY M931A2 6×6 began life as a U.S. military 5-ton tractor before Plan B Trucks of Utah converted it into a large expedition camper in 2017. The finished vehicle measures roughly 36 feet long and keeps its heavy-duty military chassis, drivetrain, air brakes, and central tire inflation system.
BMY, a division of Harsco Corporation, built the M931A2 6×6 at Marysville, Ohio, from the end of the 1980s into the early 1990s. When it was empty, an M931A2 weighed in at a hefty 19,895 lbs. Its fifth wheel carried up to 15,000 lbs of a loaded semitrailer’s weight, and the semitrailer could weigh up to 37,500 lbs with its payload.
From AM General To BMY
The M939 series succeeded the earlier M809 family, and between early 1983 and late 1993, the Army bought about 34,900 of them. They kept the basic layout of the trucks they replaced but were the first of the Army’s 5-tons to have air brakes and an automatic transmission as standard. This made them vastly easier to drive for GIs, who often didn’t get a whole lot of heavy truck driving instruction before they were put behind the wheel. The tractor version was the M931 when it came without a front winch, and it was the M932 when it came with one.
AM General built the first M939s, Pennsylvania senators Arlen Specter and John Heinz then urged the Army to set aside competitors’ complaints and award the next 5-ton contract to Harsco, of Camp Hill, Pennsylvania. On May the 14th, 1986, the Army awarded it to Arveco, a wholly owned Harsco subsidiary, in a contract announced at about $1 billion for 15,000 trucks. The contract was later transferred to Harsco’s BMY Wheeled Vehicles operation (the initials stand for Bowen-McLaughlin-York), which built the trucks at Marysville. The M939A2 started reaching U.S. Army bases in 1989.
In late 1990 Harsco agreed with the Army to increase its contract to 17,092 trucks, and an order for M939A2s followed in early 1991.
The Changes That Made The “A2”
The Army’s operator’s manual for the series describes the M939A2 (better known simply as the A2) by two key changes, the first was the engine. The M939 and M939A1 used the Cummins NHC 250, an 855 cubic inch (14.0 liter) naturally-aspirated inline six that the manual rates at 250 bhp at 2,100 rpm and 685 lb ft of torque at 1,500 rpm.
Power comes from an 8.3 liter Cummins 6CTA turbodiesel inline-six producing 240 bhp and 745 lb ft of torque, paired with an Allison 5-speed automatic and dual-range transfer case. The truck also keeps its Rockwell axles, while twin 75-gallon diesel tanks provide substantial range for long-distance travel.
The A2 was powered by the Cummins 6CTA8.3, a turbocharged and aftercooled inline six of 504.5 cubic inches (8.3 liters), with a 4.49 inch bore and a 5.32 inch stroke – the manual gives it 240 bhp at 2,100 rpm and 745 lb ft at 1,500 rpm.
The new engine was smaller, but it made more torque and used quite a bit less fuel. The manual listed approximate consumption of 5.5 to 6.0 mpg for the 6CTA8.3, against 3 to 4 mpg for the NHC 250. I know guys driving lifted big block pickups who would be envious of either set of figures.
The second change made for the A2 was its central tire inflation system, fitted to the A2 alone, which let the crew raise or lower tire pressures from the cab. The settings for A1 and A2 trucks were 60 psi for highway use, 35 psi cross-country, 25 psi in mud, sand, and snow, and 12 psi for emergencies. Being able to air the tires down from the comfort of the cab made a huge difference in places like Iraq and Afghanistan.
Built To Pull
The M931A2 shared its 167 inch wheelbase with the M929 and M930 dump trucks, it was 264.5 inches (22 ft 0.5 in) long and carried 116 gallons of fuel in two tanks. Its steel ladder frame chassis had three beam axles on heavy duty leaf springs, with locating arms for the rear tandem arrangement.
Every version of the series used the same Allison MT654CR 5-speed automatic gearbox, and behind it sat a dual-range transfer case. In low range it engaged the front axle automatically by air, and in high range the driver engaged it with a dash switch if it was needed. Steering was hydraulically assisted, as you would expect, and the brakes were a full air system with spring brakes at the rear wheels, and the electrical system ran at 24 volts.
In June of 1998 the Army counted 31,800 M939s in its inventory, 16,800 of them A2s. It expected them to serve for at least 30 years, and as a result, many of them have been slowly finding their way into civilian hands.
Inside, the camper has wood-paneled walls and flooring, a dinette, fold-down sofa, multiple sleeping areas, a full galley with induction cooktop, microwave and refrigerator/freezer, plus separate wet and dry bathroom areas.
The BMY M931A2 6×6 Overlander Shown Here
This is a 1990 BMY/Harsco 5-ton 6×6 that began life, as they all did, as a U.S. military M939-series truck before later receiving a comprehensive expedition-RV conversion from Plan B Supply/Plan B Trucks of Utah in 2017.
The military drivetrain was kept in place, including the 8.3 liter Cummins turbodiesel inline-six, Allison 5-speed automatic, Rockwell dual-range transfer case, top-loading axles, air brakes, and CTIS. Period build paperwork notes that the engine had been overhauled while still in military service in 2008.
Plan B transformed the truck with a purpose-built camper body measuring 27 feet internally, giving the completed vehicle a bumper-to-bumper length of 36 feet. Finished externally in red and black textured bedliner, it has nine flush-mounted solar panels, a powered awning, extensive exterior storage, LED lighting, a 17,500 lb front winch, and twin 75-gallon diesel tanks.
The interior is considerably more domestic, with wood flooring and wall paneling, a dinette, multiple sleeping areas, a fold-down sofa, full galley with induction cooking and refrigerator/freezer, separate wet and dry bathroom areas, diesel heating, air conditioning, and substantial fresh- and waste-water capacity. A lithium house-battery system, solar charge controllers, Xantrex inverter, and shore-power connections allow it to operate away from conventional RV infrastructure.
This truck appeared on the TV series Extreme RVs in 2017, the series followed the construction of unconventional motorhomes and expedition vehicles, so this RV would have been a perfect fit.
This is a 1990 BMY/Harsco 5-ton 6×6 that began life, as they all did, as a U.S. military M939-series truck before later receiving a comprehensive expedition-RV conversion from Plan B Supply/Plan B Trucks of Utah in 2017.
The truck has reportedly covered only about 22,000 miles, with 3,000 miles accumulated after leaving military service according to the earlier paperwork. It’s remained essentially the same large-scale expedition conversion since the Plan B build, although its house batteries and starter have been replaced more recently and it received a complete set of 395/85R20 Goodyear MV/T tires in 2026.
It’s now being offered for sale out of Golden, Colorado with a build sheet and a duplicate Idaho title in the name of the owner and their business. If you’d like to read more about it or register to bid, you can visit the listing here.
Images courtesy of Bring a Trailer
Articles that Ben Branch has written have been covered on CNN, Popular Mechanics, Smithsonian Magazine, Road & Track Magazine, the official Pinterest blog, the official eBay Motors blog, BuzzFeed, Autoweek Magazine, Wired Magazine, Autoblog, Gear Patrol, Jalopnik, The Verge, and many more.
Silodrome was founded by Ben back in 2010, in the years since the site has grown to become a world leader in the alternative and vintage motoring sector, with well over a million monthly readers from around the world and many hundreds of thousands of followers on social media.
