The bazooka is not special in itself, it is that rocket it fires that is special. inside the rocket there is a cone, and inside that cone is some superheated copper, when the rocket hits the vehicle the cone snaps inside-out shooting a spray of superheated copper through the armour of the vehicle, it is generally used to create a hole in the vehicle, not destroy it.
Air is sucked out of the bazooka and there is a seal at the end where the ammunition is fired. Then when you fire the weapon the seal at the end is released and the cone or whatever the ammunition is used flies through the air hitting the target aimed at.