This is a longer, more detailed video of the Killdozer incident -
Killdozer has been used as a nickname for the armored bulldozer constructed by Marvin Heemeyer that was used to demolish a significant portion of Granby, Colorado in June 2004
There used to be a website devoted to this incident, but I can't find it.
It described in detail the method that he used to armor this machine. It consisted of something like layer of 3 inch concrete, layer of 1 inch steel, 3" concrete, 1" steel, and another layer of concrete.
He had cameras installed for his vision, and drove it by monitor. He has also sealed it airtight and had air tanks to breathe from, along with several gun ports (Which I assume were sealable). It became apparent that he had planned on not coming out alive because he had sealed himself inside the cab. He ended up killing himself before police could get in.Wiki link