(covers information from an alternate timeline)
Captain Cray was an officer in the British Navy during the 19th century. While on a voyage, his ship was hit by a typhoon in the Pacific Ocean, and everyone back in England thought the ship would never return. Eight months later, Cray and his crew sailed into London harbor, with the remains of his tattered ship, consisting of only a few planks and half a sail, according to some accounts.
In an alternate timeline, Commander Chakotay recalled the above story, when he gave Kathryn Janeway a present for her birthday - a replica of the pocket watch worn by Cray. He thought the relation between the two was appropriate. (VOY: "Year of Hell")