This submarine doesn't need any explanation. If you read the comments there, it's just breathtaking. You can easily see why this is a an art of war. This literally changed the world of war and the acts of what nations would do.
Cutaway diagram of the USS Monitor. USS Monitor was innovative in several respects, including the first 360-degree rotating armored gun turret on an operational warship. All but 18 in of the hull was completely underwater and was protected by an armored "belt". Her keel was laid on 25 October 1861, and she was launched 118 days later.