Alright, with the confirmation of global war coming back, and the lovely waterways which it contains, I am moving to begin the brainstorming for a Submarine unit. Below are my ideas of making it useful, yet not OP.
1. Submarine Basic Strengths
1.1 The sub will utilize torpedoes as weapons which can be fired when submerged or surfaced.
1.2 The sub can only be attacked by a unit which drops depth charges or torpedoes (more to come below).
1.3 The sub is visible to all when surfaced; transparent to owner and allies when submerged. Yes, this means the sub will be stealth when underwater.
1.4 The sub shall have great vision when submerged (sonar) and shall have a moderate engagement distance.
1.5 the sub should have a strong attack against ships, rivaling or surpassing that of the destroyer.
1.6 the sub shall be unlocked after the cruiser, yet before the battleship.
1.7 the sub shall have extended range capabilities as it is meant to operate underwater for long periods of time.
2. Submarine Basic Weaknesses
2.1 the sub shall be vulnerable to bombers, yet extremely vulnerable to torpedoes and depth charges.
2.1.1 the Destroyer and Submarine shall be the only units capable of firing torpedoes.
2.1.2 the Cruiser shall deploy depth charges aft of the ship to combat the submarine.
2.2 the sub shall become "spotted" or lose stealth, even if submerged, upon launching a torpedo or being with the view range of a destroyer or cruiser (sonar capable ships)
2.2.1 Sub can re-enter stealth status after escaping enemy ship line-of-sight.
let me know what you think. Suggestions welcome.