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This would be a variant of normal battleship where the players are able to set a certain number of lighthouses to be placed on the board automatically by the computer. The lighthouses would appear after you set your ship and would be placed randomly on squares where there is no ship. Each lighthouse would display a number to the opponent, telling that opponents how many ships are in the same row or column as the lighthouse (entire ships, so a vertical battleship in the same column as a lighthouse would only be "1"). As ships in the row or column are destroyed this number drops. This would provide additional strategy regarding how you place your attacks. Of course this would be something that users could set, including set to zero to disable it entirely.

Maybe the lighthouses should be called sonar bouys as it is more fitting with their function and nature of the game. It might also be interesting if the player could set down the bouys when it's his/her turn instead of taking a shot highlighting contact in a circular section of feild?

The point about the lighthouses is they shine out a narrow beam and only along rows and columns. It is taken from the "lighthouse battleship" variant of the single-player puzzles. The idea is to give additional information to users that they will have to incorporate into their targetting strategy. It is fairly ambiguous information, but it could still radically change how they pick their targets.

As for dropping sonar, I already discussed that in [KBattleship] Special weapons and scanners