In addition to retaining greater hull strength, a four-shaft arrangement would have allowed a greater ability to steer the ship using only propeller revolutions than the three-screw system according to Ballard.[21] During Bismarck's Atlantic operation in May 1941, the ship's rudder was disabled by a torpedo hit, and her course could not be corrected by altering screw revolutions;[22] this problem had already been revealed during sea trials, but it could not be corrected.[23]