With this some part follows up with my Battleship suggestion

I felt that defensive structures for move craft are somewhat weak in a sense, there's no well armored pill boxes or even coastal artillery

So with these do note no matter what these can not be rotatable structures.

The Coastal Artillery

A defensive structure that can be in peaceful towns or nonpeaceful to help bulk up the ports power projection. Its very easy to get camped with your ships when prepping for a siege to either assaults' or defend. having a structure that can engage the enemy within peaceful claims (only in a ocean tile btw) can help aid the defense of retreating comrades or even weaken the enemy's power projection to force a blockade, it can be destroyed when fire upon. There can be classes of these defensive structures but it can also be effected by the towns size, for a example a town with a population of 1-5 there can only be 4inch guns as the coastal battery. with towns with people 10-15 can be 9's if battleships are added towns with 30+ can use 16inch cannons if not there can be 12's or 14's.

Size 500 blocks max firepower max 3 cannons uses the same blocks as turrets

Pill boxes

A defensive structure that utilizes the tank mg, one can be piloted per person. it can be placed on forts, can be used in only siege claims. is no rotatable, I figured this could be a decent option because I feel it isn't as used and could provide a different set to help people who are outnumbered potentially.

size 250 blocks max firepower 1 tank mg and uses the same blocks as turrets

If there's anything to add or any ideas plz lemme know!