With Italy's entry into World War II in June 1940 Leonardo da Vinci was dispatched to the Atlantic to Bordeaux in occupied France to serve in the Italian submarine flotilla there, BETASOM.

Leonardo da Vinci carried out 11 war patrols, sinking 17 ships of 120,243 GRT,[5] which included the 21,500-ton ocean liner RMS Empress of Canada.

In July 1942 Leonardo da Vinci was assigned to a special operation aimed at mounting raids on harbours on the eastern seaboard of the United States.

The project, first started in July 1942 by Junio Valerio Borghese, involved launching Leonardo da Vinci from the BETASOM base in Bordeaux to the mouth of the Hudson River loaded with a CA-class submarine and a team of divers armed with 28 explosive charges.

[11] On 19 March Leonardo da Vinci torpedoed and sank the 7,628-ton British cargo ship SS Lulworth Hill in the South Atlantic.