either weapons that costs a lot for weight, like antiship missiles, or target designator for friendly calital ship guns.
As in WMD system, those big capital ships, like the Harbinger, can only be 'internally damaged' by torpedoes. As well as destroying the turret/component that was designated, it also pierces the hull, causing damage to the ship itself. It could be possible to destroy the ship itself without torpedoes, but it would require some manuvering, such as flying into the hangar, blowing up the hangar wall to get to the reactor, blowing up the reactor, HGT back towards the hangar, or blow up the engines and escape. Something I find funny in Treasure Island is when the cannon is blown up, it then explodes again, probably due to a magazine or something. The first and third barrels stick straight up, whilst the second barrel is pointing down. Its as though the very cannon is flipping off the Mercs and Marines in defiance.