Didn’t Japan use mini submarines during the attack on Pearl Harbor?

Yes, they did. Japan sent five mini submarines to take part in the attacks. They were carried to the Hawaiian Islands on the larger submarines that were also part of the plan. However, they were generally a failure. Our first warning of the attack – which we obviously didn’t take seriously enough – came when we discovered one of the mini submarines trying to enter the harbor and sank it.

It was originally thought that none of the mini submarines were able to accomplish their missions. However, recent video analysis indicates that one of the small subs may have penetrated the harbor and successfully fired one torpedo against Battleship Row, hitting its target.

These very small submarines displaced only about 60 tons. They had a crew of two men and carried two torpedoes.