Everyone knows of Japan's use of kamikaze weapons in WW2 in the waning days of the war. These included suicide planes, patrol craft, and manned torpedoes, but this one I never heard about and blew my mind.
The Fukuryu was little more than a makeshift diving suit made for trained kamikaze personnel which were expected to stand in shallow water off shore of an incoming American invasion. These men carried 2 3.5 liter O2 tanks and were expected to be able to walk at a depth of 5-7 meters for a time of up to 10 hours if need be.
In combat, these men were expected to carry large sea mines on the end of a 16 foot bamboo pole. They were to wait until a landing craft were to be close by, and they were to sorta just jam the sea mine up against the hull of the landing craft until it detonated. The Fukuryu user was obviously not expected to survive the explosion.
There is 1 possible case of Fukuryu use where they are suspected of sinking a landing craft in January of 1945 and 1 attempted attack in Febuary.
https://en.wikipedia.org/wiki/Fukuryu