This cannon is fitted into the tank's hull. It can only use the cannon to shoot targets that are completely within a 90° radius of an imaginary line tangential to its front.
A hull-mounted weapon's Size rating is decreased by 1 as long as it remains hull-mounted. The Size rating cannot be decreased below 1 by this.
Any weapon can be equipped as hull-mounted, and it retains the special rule for as long as it is equipped.