The Allied invasion of Italy was the Allied amphibious landing on mainland Italy that took place from 3 September 1943, during the Italian campaign of World War II. The operation was undertaken by General Sir Harold Alexander's 15th Army Group (comprising General Mark W. Clark's American Fifth Army and General Bernard Montgomery's British Eighth Army) and followed the successful Allied invasion of Sicily. A preliminary landing in Calabria (Operation Baytown) took place on 3 September, the main invasion force landed on the west coast of Italy at Salerno on 9 September as part of Operation Avalanche at the same time as a supporting operation at Taranto (Operation Slapstick).
Background
Allied plan
Following the defeat of the Axis powers in North Africa in May 1943, there was disagreement between the Allies about the next step. British Prime Minister Winston Churchill wanted to invade Italy, which in November 1942 he had called "the soft underbelly of the axis" (American General Mark W. Clark would later call it "one tough gut"). Churchill noted that Italian popular support for the war was declining and an invasion would remove Italy from the Axis, thus weakening Axis influence in the Mediterranean Sea and opening it to Allied traffic. This would allow the reduction of shipping capacity needed to supply Allied forces in the Middle East and Far East theaters at a time when the disposal of Allied shipping capacity was in crisis, permitting an increase of British and American supplies to the Soviet Union. In addition, it would tie down German forces in Italy. Joseph Stalin, the Soviet leader, had been strongly pressuring Churchill and Roosevelt to open a "second front" in Europe, which would lessen the German Army's focus on the Eastern Front, where the bulk of its forces were fighting in the largest armed conflict in history against the Soviet Red Army.
However, U.S. Army Chief of Staff General George C. Marshall and much of the American staff wanted to avoid operations that might delay the main invasion of Europe, which had been planned as early as 1942, and which finally materialized as Operation Overlord in 1944. When it became clear that no cross-channel invasion of occupied France could be undertaken in 1943, both parties agreed to an invasion of Sicily, codenamed Operation Husky, with no commitment made to follow-up operations. After the highly successful outcome of the Sicilian campaign had become clear, both Churchill and Franklin D. Roosevelt, the U.S. President, accepted the necessity of continuing to engage the Axis before the start of the campaign in northwest Europe. Discussions had been ongoing since the Trident Conference held in Washington, D.C., in May, but it was not until late July, with the fall of Italian Fascist Prime Minister Benito Mussolini, that the Joint Chiefs of Staff instructed General Dwight D. Eisenhower, the Supreme Allied Commander in the Mediterranean theater, to go ahead.
Despite the overwhelming success of the Sicilian campaign, a significant number of Axis forces managed to avoid capture and escape to the mainland. Contemporary Axis propaganda portrayed this as a success. In late July, the fascist government fell and Mussolini was removed as head of the Italian government, envoys of which soon began approaching the Allies to make peace. It was believed a quick invasion of Italy might hasten Italian surrender and produce quick military victories over the German troops trapped fighting in a hostile country. However, Italian (and more so German) resistance proved relatively strong, and fighting in Italy continued even after the fall of Berlin in April 1945. In addition, the invasion left the Allies in a position of supplying food and supplies to conquered territory, a burden that would otherwise have fallen on Germany. As well, Italy occupied by a hostile German army would have created additional problems for the German commander-in-chief, Generalfeldmarschall Albert Kesselring.
The Allies had originally planned to cross from the island of Sicily into the "arch" area (Taranto) of the Italian mainland, envisioning a limited invasion of the Italian "boot", whence they would advance up the western coast, anticipating a strong defense by both German and Italian forces. The overthrow of Mussolini made a more ambitious plan feasible, and the Allies decided to make their invasion two-pronged by combining the crossing of the British Eighth Army under General Sir Bernard Montgomery into the mainland with the simultaneous seizure of the port of Naples further north. The range limits of Allied fighter aircraft based in Sicily reduced their choices to two landing areas: one at the Volturno River basin to the north of Naples and the other south of Naples at Salerno (though separated from Naples by the mountainous Sorrento peninsula). They chose Salerno because it was closer to their air bases. Operation Baytown was the preliminary step in the plan in which the British Eighth Army would depart from the port of Messina, Sicily, across the narrow Straits and land near the tip of Calabria (the "toe" of Italy), on 3 September 1943. The short distance meant landing craft could launch from there directly, rather than be carried by ship. The British 5th Infantry Division (Major-general Gerard Bucknall) of XIII Corps, under Lieutenant-General Miles Dempsey, would land on the north side of the "toe" while its 1st Canadian Infantry Division (Major-General Guy Simonds) would land at Cape Spartivento on the south side. Montgomery was strongly opposed to Operation Baytown. He predicted it would be a waste of effort since it assumed the Germans would give battle in Calabria; if they failed to do so, the diversion would not work, and the only effect of the operation would be to place the Eighth Army 480 km (300 mi) south of the main landing at Salerno. He was proved correct; after Operation Baytown, the British Eighth Army moved 480 km north to the Salerno area against no opposition other than engineering obstacles.
Plans for the use of Allied airborne forces took several forms, all of which were cancelled. The initial plan to land glider-borne troops in the mountain passes of the Sorrento Peninsula above Salerno was abandoned on 12 August. Six days later it was replaced by Operation Giant, in which two regiments of the U.S. 82nd Airborne Division (Major General Matthew Ridgway) would seize and hold crossings over the Volturno River. This was at first expanded to include the entire division, including an amphibious landing by the 325th Glider Infantry Regiment, then deemed logistically unsupportable and reduced to a two-battalion drop at Capua to block the highway there. The Italian surrender on 3 September led to the cancellation of Operation Giant I and its replacement by Operation Giant II, a drop of the 504th Parachute Infantry Regiment on Stazione di Furbara and Cerveteri airfields, 40 kilometres (25 mi) northwest of Rome. This was intended to aid Italian forces in saving Rome, one of the most culturally significant cities in the western world, from German razing, a condition of the Italian armistice. Because the distance from the Allied beachheads precluded any substantial Allied support of the airborne troops, Brigadier General Maxwell D. Taylor, the acting assistant division commander (ADC) of the 82nd Airborne Division, was spirited into Rome to assess the willingness of Italian troops to cooperate with the Americans. Taylor's judgment was that the operation would be a trap and he advised cancellation, which occurred late on the afternoon of 8 September after pathfinders had already taken off aboard their troop carrier aircraft.
The main landings (Operation Avalanche) were scheduled to take place on 9 September, during which the main force would land around Salerno on the western coast. It would consist of the U.S. Fifth Army, under Lieutenant General Mark W. Clark, comprising the U.S. VI Corps under Major General Ernest J. Dawley, the British X Corps under Lieutenant-General Richard McCreery, with the 82nd Airborne Division in reserve, a total of eight divisions and two brigade-sized units. Its primary objectives were to seize the port of Naples to ensure resupply, and to cut across to the east coast, trapping Axis troops further south. The naval task force of warships, merchant ships and landing craft totaling 627 vessels came under the command of Vice Admiral Henry K. Hewitt. Following the disappointing air cover from land-based aircraft shown during the battle of Gela in the Sicily landings, Force V of HMS Unicorn and four escort carriers augmented the cruisers USS Philadelphia, Savannah, Boise, and fourteen destroyers of Hewitt's command. Cover for the task force was provided by Force H under the command of Vice Admiral Algernon Willis, a group of four British battleships and two fleet carriers with destroyers, which was directly subordinate to the C–in–C Mediterranean Admiral Sir Andrew Cunningham.
In the original planning, the great attraction of capturing the important port of Taranto in the "heel" of Italy had been evident and an assault had been considered but rejected because of the very strong defenses there. However, with the signing of the armistice with the Italians on 3 September, the picture changed. It was decided to carry the British 1st Airborne Division (Major-General George Hopkinson) to Taranto using British warships, seize the port and several nearby airfields and follow up by shipping in Lieutenant-General Charles Allfrey's British V Corps and a number of fighter squadrons. The airborne division, which was undergoing training exercises in two locations 640 kilometres (400 mi) apart, was ordered on 4 September to embark on 8 September. With such short notice to create plans, Operation Slapstick was soon nicknamed Operation Bedlam.
The Avalanche plan (using less than half the troops landed during Operation Husky) was daring, considering possible resistance by six German divisions. The Fifth Army would be landing on a very broad 56 km (35 mi) front, using only three assault divisions (one American, the 36th, under Major General Fred L. Walker, in VI Corps, and two British: the 46th, under Major-General John Hawkesworth, and 56th (London), under Major-General Douglas Graham, in X Corps), and the two corps were widely separated, both in distance (19 km (12 mi)) and by the Sele River. Clark initially provided no troops to cover the river, offering the Germans an easy route to attack, and only belatedly landed two battalions to protect it. Furthermore, the terrain was highly favorable to the defender. Planning for the Salerno phase was accomplished in only forty-five days, rather than the months that might be expected. A U.S. Army Ranger force, under the command of Lieutenant Colonel William O. Darby, consisting of three U.S. Ranger battalions (the 1st, 3rd and 4th), and two British Commando units, under Brigadier Robert Laycock (consisting of No. 2 (Army) Commando and No. 41 (Royal Marine) Commando), was tasked with holding the mountain passes leading to Naples, but no plan existed for linking the Ranger force up with X Corps' follow-up units. Finally, although tactical surprise was unlikely, Clark ordered no naval preparatory bombardment or naval gunfire support take place, despite experience in the Pacific Theater demonstrating it was necessary. (Major General Walker, commanding the U.S. 36th "Arrowhead" Division, believed the defenders, from Traugott Herr's LXXVI Panzer Corps, were too scattered for it to be effective.) The element of surprise was further limited by belated discovery of naval minefields off Salerno requiring landing craft to spend two hours traveling 19 km (12 mi) from the transports to the landing beaches.
On the German side, Kesselring lacked the strength to push the Salerno landing back, and was refused two panzer divisions from northern Italy to assist him.
Operation Avalanche was planned under the name Top Hat and supported by a deception plan, Operation Boardman, a false threat of an Allied invasion of the Balkans.