So far never used to actually defend a planet but proves to be a heavy detertent from ever attacking an Imperium World. The IPDC is among the most powerful anti orbital weapon defense systems ever built by the imperium.
The Cannon is capable of creating seperate incredibly powerful bolts of energy which are fired at around 6000 rounds a minute, at one or multiple targets capable of disabling, maiming or even vaporising targets.
One reason why more often ships will be used to protect a planet is because the recoil of the IPDC is so powerful that it creates a recoil shockwave similar to that of a nuclear device. For these reasons there is a great deall of space between the turrets and the buildings.
Although not entirely known but the UGI did have a part in designing the weapon, but he wasn't affiliated with the UGI anymore when he left after he lost his citizenship and he helped design and constructed this weapon and is one of the reasons the Imperium kept building up thier military but he never told what the UGI built but he did warn the Imperium it would shake them to the core.