The Italian Co-Belligerent Navy (Marina Cobelligerante Italiana), or Navy of the South (Marina del Sud) or Royal Navy (Regia Marina), was the navy of the Italian royalist forces fighting on the side of the Allies in southern Italy after the Allied armistice with Italy in September 1943. The Italian seamen fighting for this navy no longer fought for Italian dictator Benito Mussolini. Their allegiance was to King Victor Emmanuel and Marshal of Italy (Maresciallo d'Italia) Pietro Badoglio, the men who ousted Mussolini.
The Italian Navy played an important role once the armistice was signed. Altogether, five battleships, eight cruisers, thirty-three destroyers, thirty-nine submarines, twelve motor torpedo boats, twenty escorts, and three mine-layers joined the Italian Co-Belligerent Navy. There were additionally four squadrons of seaplanes from the Italian Royal Air Force (Regia Aeronautica).