For marine archeologists and historians, few things are more thrilling than finding a long-lost shipwreck. Recently, they discovered the remains of U-111, a World War I German U-boat, at a depth of 400 feet off the coast in Virginia, where it had been intentionally sunk by the U.S. after the war.

Historians had a good idea of where the U-111 sank, but the final resting places for some warships remains a mystery.  

To identify 20 warships that sank and disappeared, 24/7 Tempo consulted a variety of historical resources on ships lost at sea. We limited our search to ships specifically built or pressed into service for combat purposes. In addition to vessels that have never been found, we’ve included some that were found many years after their disappearance. (These are the most famous shipwrecks ever found.)

Click here to see 20 warships that sank and disappeared

The ships on this list sank for various reasons, including attack by another vessel or aircraft during wartime, a raging storm, or a catastrophic mechanical problem.

More than half the missing vessels on this list are submarines; three of them sank in one year, 1968, not one of those during combat. Submarine duty is the most dangerous military service; 28,000, or 75%, of German submariners, died in World War II. (Here’s a list of the oldest ships and submarines still operating in the U.S. Navy.) 

Several missing warships on our list have notched a storied place in history. The HMS Endeavour, which Lieutenant James Cook piloted to New Zealand and Australia in the 18th century, was scuttled by the British during the American Revolution off the Rhode Island coast. The Portuguese ship Flor de la Mar, laden with what some have called the greatest treasure trove ever, likely was lost in the Strait of Strait of Malacca in the 16th century.