Pretty Please!
Its a huge step in development,
Just thinking about it is hard work, but I would do it like this.
1. Water that can boats move in, would be first along with underwater terrain (Sea Bed)
2.A Uboat, (preferably a TypeVII with Wintergarten to shoot down attacking aircraft

)
3.Detachable Destroyers, players could command the Destroyers, other players could join the ship as AAA gunners.
4. Frieghters,Tankers, Troop Transports. Like the Barges in game, these ships would sail from friendly port to port.