Enter the fascinating and elite world of secret naval units--the frogmen and commandos who waged war with midget submarines and human torpedoes. These subs, which came to prominence during World War Two, were potent weapons, better able than any other craft to penetrate deep into enemy waters and close in on unsuspecting targets. Here is their history, including the derivatives (like small submersibles), operational details, brave underwater warriors who manned them, daring attacks, and future role.