The USS Cyclops (AC-4) was a massive U.S. Navy collier (coal ship) which was last seen on March 4, 1918, departing Barbados for Baltimore on a trip originating in Brazil.
It was carrying 309 people including officers crew and passengers and a heavy cargo of Manganese ore, which was heavier and denser than coal. The ship was never seen again and its wreck has never been found. It remains the largest non-combat loss of life in U.S. Navy history.