suicide divers; underwater suicide attack unit
Historical term for a Japanese Special Attack Unit in WWII; divers equipped with explosives to attack landing craft.
The Fukuryu were one of the special attack units organized by the Imperial Japanese Navy at the end of World War II.
From 伏 (ふく, 'to lie hidden') + 龍 (りゅう, 'dragon'), literally 'hidden dragon'. The name was given to this underwater suicide attack unit.