After Italy's surrender in 1943, the Luigi Torelli was taken over by Nazi Germany's Kriegsmarine, then, in the waning months of the war, the Japanese Imperial Navy.

[7] Afterward, it conducted a short reconnaissance mission in the Gulf of Genoa, and was then dispatched to the Atlantic to Bordeaux in occupied France to serve in the Italian submarine flotilla there.

[7] The Torelli was the first submarine to be attacked by an Allied Vickers Wellington using the Leigh light, on the night of 3 June 1942 at roughly 70 miles (110 km) off the Spanish coast, suffering considerable damage but managing to reach the port of Avilés and, after an attempt to reach Bordeaux ended when an Australian Short Sunderland attacked the submarine and inflicted further damage upon it, it ended up in Santander; after emergency repairs, the submarine managed to exit the port (where the Spanish authorities intended to intern it) with a stratagem, and safely reached Bordeaux on July 15.

The Italian boats, due to their dimensions, were deemed better suited for long voyages to the Far East on missions to acquire precious and rare material.

The Luigi Torelli and sister submarine Comandante Cappellini were the only two ships to fly the flags of all three main Axis powers during World War II.

As the I-504, Luigi Torelli's crew claimed to have shot down a B-25 Mitchell bomber while under the Japanese flag near the very end of the war in the Pacific, allegedly the last success by an Axis naval vessel in the conflict.