Naval mines

I would suggest naval mines as a new type of weapon in Call of War.
Its purpose would be to prevent or reduce the mobility of the enemy navy by undermining naval routes and denying access to a certain maritime area. These mines could also be placed at the entrance to a port or a strait.
The units that would have the ability to launch/remove/destroy mines would be:
Navy:
Minelayer: with the function of deploying naval mines.
Minesweeper: would have the function of removing/destroying enemy naval mines. They could reveal mines of the same level or lower.
Submarines: they would also have the function of deploying naval mines but the destruction power would be less because they carry less amount of mines inside.
Optionally the minelayer and minesweeper could be a single type of ship that aggregated both functions, that the game developers would decide.
the level of the naval mines would be the same as the vessel that launched them.
Aircraft:
Tactical Bomber: would have the function of launching naval mines through the air.
Naval Bomber: It would have the ability to launch mines from the air and to reveal enemy naval mines of the same or lower level. 

Naval mines would be stealth revealed by naval bomber or minesweeper. They would be revealed otherwise when ships hit them.