There are three of them in existence, until the player destroys them all in the mission "Destroy the Behemoth".
The Behemoth is the largest police vehicle. It has two cockpits and six wheels.
Each one is assigned to a single large road in the Police State. Due to their size they cannot roam freely; instead they travel slowly up and down their road, back and forth (hence the two cockpits). An unwary player can be crushed under its giant wheels. In the mission where it must be wasted, it can fire homing missiles to defend itself.
The Behemoth has a weakness; one side of the roof has an exhaust vent. The whole vehicle can be put out of action if a Bomb is shoved down this vent.