The Mediterranean inventory includes five battleships, fourteen cruisers, numerous destroyers and torpedo boats, and 45 submarines. Nineteen of those submarines are concentrated around Bizerte and Sousse in Tunisia. Combined with British boats from Malta, they can attack Italian convoys from both sides of the narrow supply route to Libya. French North Africa also threatens Libya on land, so Italy must defend its rear even before an Allied ground offensive begins.
Chapter · 18:26-20:22
The Mediterranean fleet and Tunisia's submarine threat
French ships and submarines based around Tunisia turn Italian supply routes to Libya into a severe operational vulnerability.