Marvin John Heemeyer, an American welder and an automobile muffler repair shop owner most known for his rampage with a modified bulldozer. Outraged over the outcome of a zoning dispute, he armored a Komatsu D355A bulldozer with layers of steel and concrete and used it to demolish the town hall, the former mayor’s house, and other buildings in Granby, Colorado. The rampage ended when the bulldozer got stuck in the basement of a Gambles store he was in the process of destroying. Heemeyer then killed himself with a handgun.
The machine used in the incident was a Komatsu D355A bulldozer fitted with makeshift armor plating covering the cabin, engine and parts of the tracks. In places this armor was over 1 foot (30 cm) thick, consisting of 5000-psi Quikrete concrete mix sandwiched between sheets of tool steel, to make ad-hoc composite armor.
This made the machine impervious to small arms fire and resistant to explosives: indeed three external explosions and more than 200 rounds of ammunition fired at the bulldozer had no effect on it.
For visibility the bulldozer was fitted with several video cameras linked to two monitors mounted on the vehicle’s dashboard; the cameras were protected on the outside by 3-inch (76 mm) shields of bullet-resistant plastic. Onboard fans and an air conditioner were used to keep Heemeyer cool while driving, and compressed-air nozzles were fitted to blow dust away from the video cameras. He had made three gun-ports, fitted for a .50 caliber sniper rifle, a .308 semi-automatic, and a .22 long rifle, all fitted with a half-inch-thick steel plate.
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Heemeyer apparently had no intention of leaving the cabin once he entered it. Authorities speculated he may have used a homemade crane found in his garage to lower the armor hull over the dozer and himself.