The_Damned is right capships need the CM's most big ships in all navy's have at least some form of CM to stop missiles. Sure they also have the goalkeeper defence guns too but come on, it's hard enough to hit a missile using the 8.33 refire weps let alone the chainguns.
The torpedo idea would probably be best for the destroyers, as they typically use them to compensate for their lack of the heavier guns that cruisers and BS's can mount.
The britonia destroyer is pretty weak with just 7 turrets, one of which can only fire forward, the only way to get 6 turrets on it to fire at the same time is having a target below and behind it. So perhaps it could have a destroyer forward gun, or some torpedo mounts, the kusari destroyer has nearly twice as many turrets, of which none are locked to fire in one direction.