Surfaced- The Sub can be damaged, but can build up air supplies for underwater sailing
- Submerged - The sub cannot be damaged by shells shot by guns, but torpedoes can hit it . BB and CA cannot detect them.
- Critical Dive - The sub cannot be hit by ANYTHING. But the sub cannot move, shoot, and the DP of the ship is lowered while in CD.
A submarine has the ability to stealthily attack a capitol ship, such as a battleship, Heavy Cruiser. All ships (excluding FFs, DDs, and other subs) have a very limited detection system for submarines.
Early submarines (such as a Type II) have a very slow speed, air supply replenishment, and need many crewmen to function with a high efficiency. Also, when attacking large battleships early submarines don't have a very large impact (starting from BB3+). They may lower the DP a few thousand, but then they usually run out of air, then surface, and pummeled by Battleship guns.