Fishing trawlers and such, (spy ships) as well as oilers,convoys, you name it,, it would be cool!
All of it should be able to be destroyed,, no need to be controllable ,, the spy ships should have small radar and flash when detected but delayed for a short period to reflect com. Problems,,, they might not even show up on the map unless they are flashing,, just a red dot on the map flashing,, wouldn't tell you much but might save your base from an NOE, or a sneaky CV!