Among the numerous assault crafts invented or experimented by the Decima Flottiglia MAS, the "Siluro a Lenta Corsa" (SLC -slow running torpedo) dubbed "maiale" - pig - by the crews, received great consents and was developed with great determination. The SLCs had been conceived as micro-submarines driven by two frogmen and able to overcome obstructions and anti-submarines nets in the harbours and also able to position the explosive charge directly under the hulls of the enemy ships.
Obviously it was necessary to take such underwater warriors next to the enemy bases : therefore a transport vehicle defined "approacher" was required. Certainly the "approacher" for excellence was the submarine.
For this reason, after the first months of war, three submarines 600 class, (two "Adua" and one "Perla" type) were modified and equipped for the role of "approacher". The gun on the deck was removed and three watertight containers were positioned to hold the SLCs (before and behind the tower).
The success obtained in the Mediterranean Sea by the SLCs transported by the Scirč and by the frogmen "Swimmers Gamma" stimulated in 1942 the MAS technicians to plan some attacks to New York, Freetown and St. Paul of Brazil harbours.
The project was ambitious, and above the technologies of the period. Obviously the "approacher" had to be a submarine but evidently SLCs could not be employed. In fact, besides the difficulties to transport them along the Atlantic route of 11,000 kms, what was required was a craft able to return back into the submarine after the mission (in the Mediterranean the Decima had pre-arrenged an efficient recovery-service for those men returning to Italy by land or by air ).
This microsub, it was a torpedo 533 mms with an electric motor. The craft can transport two frogmen and one explosive charge from 220 kgs (in the last versions the explosive charge was of 300 kgs). This charge was contained in the anterior part and it was detachable from the "pig" to be applied on the submerged hull of the hostile ship.
Planned in 1935 from the Genio Navale of Italian Navy, it was operational only from the end of 1940. In 1943 it was in phase of testing a improved version (S.B.B.) not operational because of the armistice.
From this site:
http://www.subnetitalia.it/decimaslc.htm
