Well technically it's not a tank, but an "armored personnel carrier." It belongs to the Sheriff's Department of Richland County, South Carolina. Sheriff Leon Lott has named it "The Peacemaker" and it apparently uses a caliber of ammunition that's generally only reserved for use against armored vehicles. Sheriff Lott insists the tank will "save lives."
As someone aptly commented on boingboing, "This may be a microcosm of everything that is wrong with our country distilled into one purchase."