User blog comment:RandomGuy96/So how do planetary defense cannons work?/@comment-5436239-20130129005827

Oh, and I would never make a canon with the purpose of taking out main battleships, cruisers, and dreadnoughts. The cannons would be most effective on small craft carrying soldiers and enemy personnel. While I would focus these weapons to attack a ship if necessary, but if I know they will not bombard my defensive point, I will tear their men from the sky(This would work for when Reapers harvest, slavers raid, or in the case of standard warfare, so basically everything unless they are focused on Total Warfare).

They would be forced to send in special teams to deal with the PDCs, like on Virmire.