The Bretonian gunboat is weird yeh, I mean, you could make it into a light destroyer like the liberty cruiser (probably what it was intended for), but then Bretonia has no gunboat (though that doesnt bother me that much, effects privateers though).
The Forward gun on the Bretonian gunboat is REALLY big, compare it to say, the kusari gunboat forward gun, and it looks as if it could do as much damage as a Liberty cruiser. The shape is still also a SN magnet even as a Destroyer, the Kusari destroyer would still be superior in dodging/agility.
So yeah, I think it should be made into a destroyer, always have done.
PS: opps, off topic, well the kusari destroyer isnt broken in cap vs cap engagements, bit stupid against bombers and gunboats, and I can see battleships having a hard time, though not likely impossible at all, spam missiles? heh.
