A submarine ace (subsea ace, undersea ace, sub ace, U-boat ace) is a submarine commander who has sunk 100,000 tons or more in kills. In World War I, U-boat commanders upon sinking 100,000 tons became U-boat aces. In World War II, U-boat commanders upon sinking 100,000 tons and becoming U-boat aces, were awarded the Knight's Cross of the Iron Cross (RK), under the points system instituted by Adolf Hitler. Those who exceeded 200,000 tons were eligible for the Knight's Cross to the Iron Cross with Oak Leaves