On July 26, 1943, the day after Nazi ally Benito Mussolini is deposed by Italy's Grand Council—who nominally claim they will keep fighting with the Germans—Adolf Hitler calls the act "naked treachery." In a military briefing at his headquarters, the Führer declares the Italians are buying time before negotiating surrender terms with the WWII Allies and calls for immediate action, including the German occupation of Rome.
Hitler had feared that such a turn of events was possible, if not probable. Hitler had come to Italy on July 19 to lecture Il Duce on his failed military leadership—evidence that he knew, even if he was not admitting, that both Mussolini and Italy were about to collapse, leaving the Italian peninsula open to Allied occupation. Despite a half-hearted reassurance from Mussolini that Italy would continue to battle on, Hitler nevertheless began preparing for the prospect of Italy’s surrender to the Allies.
When Mussolini was ousted from power and arrested by his own police six days later. Hitler gathered Goering, Goebbels, Himmler, Rommel, and the commander in chief of the German navy, Karl Doenitz, at his headquarters to reveal the plans of action he had already been formulating. Among them: (1) Operation Oak, in which Mussolini would be rescued from captivity; (2) the occupation of Rome by German forces and the reinstallation of Mussolini and his fascist government; (3) Operation Black, the German occupation of all Italy; and (4) Operation Axis, the destruction of the Italian fleet (in order to prevent it from being commandeered for Allied use).
Hitler’s advisers urged caution, especially since it would require recalling troops from the Eastern front. The Allies had not made a move on Rome yet, and although Mussolini was under arrest, the Italian government had not formally surrendered. Germany had received assurances from Mussolini’s successor, , that Italy would continue to fight at Germany’s side. But Hitler had no faith in that promise, calling Badoglio "our grimmest enemy."
In early September, 1943, Allied forces launched an invasion of the Italian mainland, and within a week, Italy surrendered unconditionally. On October 13, Italy declared war on its former ally Germany, becoming a co-combatant with the Allies.
