The disappearance of the USS Cyclops
The Navy collier USS Cyclops was last seen at Barbados on 4 March 1918, bound for Baltimore, and was never found.
Military.com describes the USS Cyclops as a ship 540 feet long and 65 feet wide, armed with machine guns, that brought medical staff and provisions to American troops in France in wartime. Barbados was the last place anyone saw it, on 4 March 1918.
The North Carolina Department of Natural and Cultural Resources adds that the Cyclops was bound for Baltimore, running slowly with engine trouble. Radio contact ended the same day. In April, Navy officials told the Associated Press the ship was overdue. French ships and American ships searched the shipping lanes linking the two ports and turned up nothing of the ship or the people aboard.
Several explanations have been offered. Wikipedia reports a theory of catastrophic structural failure and describes a Bermuda Triangle attribution as a more outlandish one. The Navy's own history office, quoted by Military.com, recalls that the magazine Literary Digest speculated a giant octopus pulled the ship under, and that another theory held that a freak storm suddenly capsized it with all hands inside.
"In both cases, their loss was theorized to have been the result of catastrophic structural failure,[19] but a more outlandish theory attributes all three vessels' disappearances to the Bermuda Triangle.[20]"
- The Mystery of the Vanished USS Cyclops Still Unsolved 100 Years Later, Military.com (2018)
- USS Cyclops: Lost at Sea, 1918, North Carolina Department of Natural and Cultural Resources