Sailors' slang for the bottom of the ocean. Someone drowned at sea may be said to have “gone down to Davy Jones's Locker.”
Davy Jones's locker
Also, Davy's locker. The bottom of the sea, especially the grave of those who die at sea. For example, Caught out at sea during the hurricane, they thought they were heading for Davy Jones's locker. This term, first recorded in 1726, alludes to Davy Jones, a name given to the evil spirit of the sea. The ultimate origin of both Davy and Jones is disputed. A logical theory is that Jones referred to the biblical Jonah who was swallowed by a whale, and Davy was a corruption of a West Indian word for "devil."