I really love this, keep it coming. Scharnhorst is a very good choice for a limited initial release.
You can limite the map to the Arctic ocean (Easy environment to code, with very few coastal cities) and create a campaign based on exits to hunt detected convoys and stragglers. Help from Luftwaffe and UBoats as well as your destroyers or other battleships, and the permanent risk of meeting a british task force can make for a hugely intense gameplay.