Allied invasion of Italy

At the Casablanca Conference in early 1943, British Prime Minister Winston Churchill had tried to convince US President Franklin D. Roosevelt of the idea of beginning the attack on "Fortress Europe" with an assault from the south on Sicily. Churchill argued that in order to proceed, it was necessary to secure the shipping lanes in the Mediterranean. Moreover, Italy could be persuaded to break away from the Axis front in this way. At the Trident Conference in May 1943, agreement was reached in principle to continue operations in the Mediterranean in 1943 with the aim of bringing about Italy's withdrawal from the war. This was intended to improve the prospects of Operation Roundup, planned for 1944, since the German Army would be forced to commit additional divisions to occupy the Balkans and defend northern Italy and southern France. The Allied commander in chief in the Mediterranean Theater of Operations General Dwight D. Eisenhower was then tasked with developing options for follow-on operations for Operation Husky. The Americans originally favored a landing on Sardinia and Corsica and an intensification of the air war, while the British advocated a landing on the Italian mainland with the option of later establishing a bridgehead in Albania.

Operation Husky against Sicily began on 10 July 1943 and was successfully completed by mid-August. At the suggestion of American Chief of Staff George C. Marshall, planning began in mid-July for an operation to capture the port of Naples under the name Operation Avalanche.

After a meeting of the Great Fascist Council on July 25 deposed Italian dictator Benito Mussolini, his successor Pietro Badoglio began negotiations for a separate peace with the Allies. At the Quadrant Conference in August 1943, Churchill and Roosevelt decided to continue operations on the Italian mainland.

Previously, the German High Command had decided to station additional German divisions in northern Italy and near Rome in order to be able to disarm the Italian army in the event of a separate peace by the new Italian government. The plans for this and for the takeover of the Italian occupied territories in the Balkans and in southeastern France were worked out under the heading "Fall Achse" (Axis Case).

While the U.S. 7th Army remained in Sicily, the British 8th Army, also involved at Husky, commanded by General Bernard Montgomery, and the U.S. 5th Army, deployed in North Africa and commanded by General Mark W. Clark, were designated for the landings and combined into the 15th Army Group. The British Field Marshal Harold Alexander, who was also Eisenhower's deputy, had the supreme command.

Opposing them was the German 10th Army of General Heinrich von Vietinghoff under the commander-in-chief for southern Italy GFM Albert Kesselring. It was reinforced in August by the units of the XIV Panzer Corps evacuated from Sicily.

Due to Italy's impending exit from the war, Allied commanders decided to conduct the main landing on the west coast of Italy. The landings in Calabria via the Strait of Messina and in the Gulf of Taranto were planned as secondary operations to make the German defences more difficult.

The British 8th Army was to land from Messina on the opposite coast of Calabria at Reggio Calabria on 3 September (Baytown). This operation could be carried out with light landing craft due to the short distance.

The Gulf of Salerno south of Naples was selected as the landing point for the main landing (avalanche) planned one week later, since better conditions were to be expected there than in the estuary of the Volturno northwest of Naples, which was also being considered. For this the 5th U.S. Army, consisting of the American VI Corps and the British X Corps with the 82nd U.S. Airborne Division in reserve, were selected, transported by sea from North Africa. A plan to use the 82nd Division to occupy airfields near Rome (Operation Giant II) was dropped at short notice when it became clear that the Italian Army would not side with the Allies.

The British 1st Airborne Division was to conduct simultaneous landings at Taranto (Slapstick) as a diversionary maneuver for Avalanche.