The Regia Marina had roughly 115 submarines on paper, about 84 operational at the start of the war, and often kept 25 to 30 at sea. Germany fought primarily an economic raiding campaign, whereas Italy had to move and protect convoys in a confined Mediterranean war. Submarines could deny access and act like mobile minefields, but surface escorts were still necessary to exercise sea control by moving troops and supplies safely. The force totals expose the problem of balancing raiding assets with ships that could use and secure the sea.
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Why Italy needed more than a vast submarine fleet
Italy entered the war with one of the world's largest submarine forces, but submarines could deny enemy movement without securing Italy's own Mediterranean supply routes.