Submarines have since their introduction been key during naval warfare, and indeed played an important role during World War II. From Allied subs to German U-boats, naval fleets would not be the same without them. Though just as planes crashed and ships sank, many submarines and their crews also met their fate during the war. Some of them, however, simply disappeared without a trace.
In this gallery, we look back at some of the WWII subs that disappeared for unknown reasons, and still have never been found. Click on to discover them.