Here at LSOZI, we have talked about several of the Italian and German midget subs of WWII, including a whole Warship Wednesday dedicated to the spooky little craft that sank the HMS/ORP Dragon off Normandy and another on the Italian explosive motorboats that crippled HMS York.
With that being said, I recently ran into two things you guys would find interesting. Below is a great 26-minute Oct. 1945 newsreel on German and Italian sneak attack that was recently archived by the AP:
The second is a write up by H I Sutton over at Covert Shores on the Untersee-Gleitflächen-Schnellboot Manta, a craft I had never even heard of until now.
The designers hoped to combine the transit speed of a speedboat with the stealth and survivability of a submarine. To do this it would need to combine several advanced technologies which Germany had been developing. Air Independent Propulsion (AIP) and hydrofoils.