- Mary Celeste: the brigantine set sail from New York harbor for Genoa, Italy, on Nov. 5. A British brigantine, the DeGratia, discovered the ship derelict on Dec. 5 and boarded her. Everyone aboard the Mary Celeste had vanished—her captain, his family, and its 14-man crew. The ship was in perfect order with ample supplies and there was no sign of violence or trouble. The fate of the crew remains unknown.
- USS Cyclops: the navy coal ship, used to deliver fuel and other supplies to U.S. battlefleet during World War I, disappeared while en route from Brazil to Baltimore. The ship docked briefly at Barbados on March 3–4. When it failed to arrive in Baltimore on March 13, a search was made, but neither her wreck nor any of the 309 people aboard were ever found, and the cause of her loss remains unknown.
- Köbenhavn: five-masted Danish steel barque, a sail-training ship with a crew of 75 including 45 boy cadets, sailed from the River Plate for Melbourne, Australia, on Dec. 14. The last radio contact with the ship was made on Dec. 22 and all was well. The Köbenhavn and its crew disappeared without a trace and no one knows what happened to it.