Italian Navy unit 'Decima Flottiglia MAS.' (The first SEALs)
March 25, 1941: The Italian destroyers Crispi and Sella depart Leros island in the Aegean at night, each carrying 3 small (2-ton) MTM (Motoscafo da turismo modificato) motor assault boats of the Decima MAS. Each MTM (nicknamed barchini or "little boats") carries a 300 kg (660 lb) explosive charge in its bow. The one-pilot craft are launched by the destroyers 10 miles off Suda Bay, Crete, where several British Royal Navy warships and auxiliary ships are at anchor. The MTMs are specially equipped to make their way through obstacles such as torpedo nets; the pilot steers the assault craft in a collision course at his target ship, and jumps from his boat before impact and warhead detonation. Once inside the bay, the six boats locate their targets: the heavy cruiser HMS York, a large tanker (the Norwegian Pericles of 8,300 tons), another tanker, and a cargo ship. Two MTMs hit the York amidships, flooding her aft boilers and magazines. The Pericles is severely damaged and settles on the bottom, while the other tanker and the cargo ship are sunk. The other barchini apparently miss their intended targets, and one of them is stranded on the beach. All six of the daring Italian sailors are captured. The disabled York is later scuttled with demolition charges by her crew before the German capture of Crete, while the Pericles sinks in April 1941 enroute to Alexandria.
December 3, 1941: The Sciré departs La Spezia carrying three manned torpedoes. At the island of Leros in the Aegean Sea, six Decima MAS crewmen come aboard, including Lieutenant Luigi Durand de la Penne. On December 19 Sciré releases the manned torpedoes 1.3 miles from Alexandria commercial harbor, and they enter the harbor when the British open their defenses to let three of their destroyers pass. After many difficulties, de la Penne and his crewmate Emilio Bianchi successfully attach a limpet mine under HMS Valiant, but have to surface as they attempt to leave and are captured. Questioned, they refuse to speak, and are detained in a compartment aboard Valiant. Fifteen minutes before the explosion, de la Penne asks to speak to the Valiant's captain, informs him of the imminent explosion, but refuses to give other information. He is returned to the compartment, but both he and Bianchi are not injured by the detonation of the mine. The other four torpedo-riders are also captured, but their mines sink the Valiant, the battleship Queen Elizabeth, . Although the two battleships sink in only a few feet of water and are subsequently refloated, they are out of action for over one year. The tanker Sagona was also sunk, and the destroyer HMS Jervis badly damaged.
(Other Operations as well, with 'Gamma Torpedoes' or Pigs as they were known.)
Link: to more info on operations & background on the unit!
http://en.wikipedia.org/wiki/Decima_Flottiglia_MAS#Chronicle_of_Operations