Following the defeat of the Axis Powers in North Africa in May 1943, there was disagreement between the Allies as to what the next step should be. The British Prime Minister, Winston Churchill, in particular wanted to invade Italy, which in November 1942 he called "the soft underbelly of the axis" (and General Mark W. Clark, in contrast, later called "one tough gut"). Popular support in Italy for the war was declining, and he believed an invasion would remove Italy, and thus the influence of Axis forces in the Mediterranean Sea, opening it to Allied traffic. This would reduce the amount of shipping capacity needed to supply Allied forces in the Middle East and Far East at a time when the disposal of Allied shipping capacity was in crisis and increase British and American supplies to the Soviet Union. In addition, it would tie down German forces. Joseph Stalin, the Premier of the Soviet Union, had been pressing 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 the U.S. Army Chief of Staff, General George Marshall, and much of the American staff wanted to avoid operations that might delay an invasion of Europe, discussed and planned as early as 1942, 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, it was agreed to invade Sicily, with no commitment made to any follow-up operations. However, both Churchill and Franklin D. Roosevelt, the U.S. President, accepted the necessity of Allied armies continuing to engage the Axis in the period after a successful campaign in Sicily and before the start of one in northwest Europe. The discussion continued through the Trident Conference in Washington in May but it was not until late July, after the course of the Sicilian campaign had become clear and with the fall of Benito Mussolini, the Italian Prime Minister and fascist leader, that the Joint Chiefs of Staff instructed General Dwight D. Eisenhower, the Supreme Allied Commander in the Mediterranean Theater of Operations (MTO), to go ahead at the earliest possible date.
Joint Allied Forces Headquarters (AFHQ) were operationally responsible for all Allied land forces in the Mediterranean theatre, and it was they who planned and commanded the invasion of Sicily and the Italian mainland.
The Allied invasion of Sicily in July 1943, codenamed Operation Husky, was highly successful, although many of the Axis forces managed to avoid capture and escape to the mainland. The Axis viewed this as a success. More importantly, in late July, a coup deposed Mussolini as head of the Italian government, which then began approaching the Allies to make peace. It was believed a quick invasion of Italy might hasten an Italian surrender and produce quick military victories over the German troops that could be 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 which 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 (C-in-C), Generalfeldmarschall Albert Kesselring.
Prior to Sicily, Allied plans envisioned crossing the Strait of Messina, a limited invasion in the "instep" area (Taranto), and advancing up the toe of Italy, anticipating a defense by both German and Italian forces. The overthrowing of Mussolini and the Fascisti made a more ambitious plan feasible, and the Allies decided to supplement the crossing of the British Eighth Army, under General Bernard Montgomery, with a seizure of the port of Naples. Although the Americans favored Napoleon's maxim that Italy, like a boot, should be entered from the top, the range limits of Allied fighter planes based in Sicily reduced Allied choices to two landing areas: one at the Volturno River basin and the other at Salerno. Salerno was chosen because it was closer to air bases, experienced better surf conditions for landing, allowed transport ships to anchor closer to the beaches, had narrower beaches for the rapid construction of exit roads, and had an excellent pre-existing road network behind the beaches.