Top: Handy-sized Mediterranean boats, then-strong ‘Adua’class were named after places in Italian North Africa. Boats of the class were modified to SLC human torpedoes carriers. Two of these were converted to carry SLCs and one of these the Sore, was particularly successful. She attacked Gibraltar on no less than four occasions, the raid of September 1941 accounting for two ships, including the auxiliary tanker Denbydale. Her greatest coup, however, was in December 1941 when her three SLCs put the battleships HMS Queen Elizabeth and HMS Valiant, together with a tanker, on the bottom of Alexandria harbour. She was finally sunk by the anti-submarine trawler May outside Haifa in August 1942.

Bottom: A more powerful ‘Adna 7 ‘Perla ‘ with reduced tower, Acciaio was lead boat of a class of 13. She was sunk by HM Submarine Unruly on 13 July 1943.

Italian submarines were of four basic types: very large oceangoing cruiser submarines, large minelayers, large long-range patrol boats, and medium-size vessels. The cruisers were few in number and proved rather unsuccessful, especially as they were slow to dive; they saw little operational service. The minelayers were much more successful. They displaced between 1,054 and 1,305 tons standard on the surface, with a range of 8,500 miles at 9 knots on the surface, a submerged endurance of 60 hours at 2 knots, and a diving depth of 330 feet. Armament included a battery of 6 to 8 torpedo tubes with 8 to 14 torpedoes, 36 mines, and 1 or 2 3-inch deck guns.

The 2 series of patrol submarines emerged as essentially standard designs immediately before the war began. The larger group displaced between 920 and 1,000 tons standard on the surface, with a range of 9,000 miles at 8 knots on the surface, a submerged endurance of 60 hours at 2 knots, and a diving depth of 330 feet. Armament included a battery of 8 torpedo tubes with 12 torpedoes and 1 4-inch deck gun. The smaller group displaced between 650 and 680 tons standard on the surface, with a range of 5,000 miles at 8 knots on the surface, a submerged endurance of 60 hours at 2 knots, and a diving depth of 330 feet. Armament included a battery of 6 torpedo tubes with 12 torpedoes and 1 4-inch deck gun. These smaller patrol submarines were very successful boats and performed well in the shallow, clear waters of the Mediterranean. The larger boats performed quite effectively in the Atlantic.