In the 1950s, LeTourneau Inc. developed several overland trains, essentially oversized semi-trailer trucks that could travel over almost any terrain. Their intention was to be able to handle logistics needs without being dependent on local road or rail systems, allowing them to operate in back-country areas. The US Army had three experimental units built, the largest reaching almost 600 feet (183 m) long, which holds the record for the longest off-road vehicle.The Mark II had a much larger six-wheeled cab that was over 30 feet (9.1 m). The turbine engine was much smaller than the diesel it replaced, allowing the interior to support a crew of six with sleeping quarters, toilets and a galley. It was even equipped with a radar. An additional two power cars and ten cargo cars were built for testing. In total the train now stretched over 570 feet (170 m). On flat ground it could carry 150 tons of cargo at about 20 mph. Range at full load was normally 350 to 400 miles (560 to 640 km), but additional fuel trailers could be added to extend it.The Mark II retains the record for the longest offroad vehicle in the world.