u-boat was another ship's cat aboard a royal navy ship in the second world war. whenever his ship came into port, u-boat would take shore leave (he would leave the ship to do things on shore). he would spend days on shore, and usually would return only just before his ship sailed away. one day, u-boat did not return in time for roll call and his ship was forced to sail away without him. as the ship pulled away, u-boat was seen running down the dock after the sailing ship. he made a death-defying leap onto the ship and made it aboard. the crew thought that he seemed unafraid by what had just happened, and calmly started to wash himself on deck. the crew members were very happy that u-boat had come back, since they thought he brought them good luck.