[3] Italy's entry into World War II in June 1940 found Tazzoli in operations in the western Mediterranean.

Operations during the autumn and winter of 1940 showed the Italian vessels were ill-suited to conditions in the North Atlantic, so the spring 1941 saw a change in strategy by Admiral Donitz, the German U-boat Commander (BdU).

The BETASOM boats were assigned to long-distance patrols into the mid and south Atlantic, in a bid to spread the commerce war further afield.

During this period Tazzoli was commanded by Carlo Fecia di Cossato, one of Italy's foremost naval officers.

In December 1941 Tazzoli was involved in the rescue of the crews from the German commerce raider Atlantis and the supply ship Python, both sunk by British cruisers in the South Atlantic.

With her sister ships Calvi and Finzi, she brought home over 200 survivors, a journey of several thousand miles and regarded as an epic of maritime rescue.

In March 1943 Tazzoli was handed over for conversion to a submarine transport, for blockade-running to the Far East, and her commander received a new posting.

Tazzoli is credited with sinking 18 ships, for a total of 96,650 GRT, making her the highest-scoring Italian submarine after Leonardo da Vinci.