I found this entirely by accident surfing the net!

Captain Killdozer
Unfortunately you can't always tell who those people are until it's too late and such was the case with Marvin Heemeyer. He lived in a little town in Colorado with a population of about 500. He was a welder and owned a muffler repair shop and, presumably for a while, he was a totally non-sinister individual who never even considered doing anything crazy like building a massive, nearly indestructible machine of terror.

Then, Heemeyer wound up in a dispute over his land with a cement manufacturing plant. He leased his business to someone else and sold his property while the new owners gave him six months to vacate. It was during that six months that Heemeyer built a death machine, a Komatsu D335A bulldozer outfitted with armor plating over the cabin and engine.

The armor in some places was over a foot thick and had concrete between sheets of steel, making it pretty much unstoppable. The tank was also outfitted with onboard cameras and monitors in the cabin so Heemeyer could see where he was going. The inside was made nearly airtight to resist a potential gas attack and had air conditioning, food, water and life support. Once he got in Heemeyer had no plans to actually leave the bulldozer.

Outside, the bulldozer had .50 caliber semi-automatic rifle mounted on the back, and three other semi-automatics mounted elsewhere. Basically, this was a machine designed to make everyone in his town of 500 take one massive, synchronized fear sheesh the moment it rolled out of his workshop.

Heemeyer took his machine of insanity out for a spin on June 2, 2004 by crashing it through the wall of his workshop. He then plowed through the concrete plant, the town hall, the local newspaper, a judge's house, a hardware store owned by a guy who had pissed him off, and seven other buildings, causing about $7 million in damages.

The bulldozer, which came to be known as the Killdozer since that really is the only appropriate name for it, was hit with over 200 rounds of ammunition and three small explosions that barely left a scratch on it.

Eventually the Killdozer got stuck in a basement and the engine failed. A single shot was heard in the cabin. While Heemeyer took the easy way out, and it still took authorities twelve hours to cut their way into the machine. Surprisingly, Heemeyer had not rigged the dozer to then self-destruct and destroy the entire town.

Youtube vid
http://www.youtube.com/watch?v=PZbG9i1oGPA&feature=related
a little more detailed
http://www.youtube.com/watch?v=yJcB1_EogXc&feature=related

Q:Should some Police depts have RPGs on hand??

Seems like every Xmas those stories emerge about "man takes out family , Then self!
(How come they never start with the last part first?)