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Despite having the largest submarine fleet at the beginning of the war, most of the italian subs were either "average" in performance or hampered by their use in the mediterranean sea.

The few that got out in the Atlantic or Indian ocean operated individually as commerce raiders.

There were a few notable exceptions. The 600 class got famous because of X MAS, a special corps of marines which pioneered the use of frogmen to assault every major british harbor in the Mediterranean. The italian equivalent of U-47 is the "Sciré", a 600 class submarine which snuck inside Alessandria harbor time to sink Queen Elizabeth (though, it was raised from the shallow waters and put into service again by the end of the war) and Gibraltar 4 (!) times.

Another famous sub was the atlantic commerce raider Leonardo da Vinci which has the highest success rate for an italian boat: 116000GRT of which 58000 in a single mission (thus earning a place in the top ten most successful missions of axis submarines)

Italians also built large resupply submarines and long range cruisers with 14 (!) torpedo tubes but most of them were captured after 1943 and sunk or simply remained moothballed for the rest of the war