The Allied landing at Salerno on 9 September 1943 coincided with the proclamation of the armistice of the Kingdom of Italy and marked the beginning of the liberation campaign of the Italian mainland. It failed to enforce a quick advance to Rome and gave way to the bloody operations centred around Monte Cassino.

The Allied invasion of the Italian peninsula started on 3 September 1943 with minor landings in the toe of Italy, with the intention to divert the Germans from the main invasion area near Salerno. On 9 September, one day after the Italians had signed the armistice, the Allied main force landed at Salerno (Operation Avalanche). The invasion force, under command of General Mark Clark, comprised of the U.S. 5th Army, the 82nd Airborne Division and the British X Corps.

Prior to the landing no preparatory bombardment was executed in order to secure the element of surprise. This however proved to be in vain. The Germans had defensive troops in the area. Despite this setback the Allies managed to land and secure a 35 mile broad beachfront. On 12 September the German 10th Army counterattacked the bridgehead; it could barely be held.
The German counterattack led to heavy casualties and, at some points, reached the beaches. In the end the German counterattack failed because Hitler refused Field-Marshal Kesselring to employ more troops.

For the Allies Operation Avalanche did not bring the quick advance through Italy that was hoped for. They were stopped at the German Gustav Line, centred around Monte Cassino. Rome itself was not reached before 4 June 1944. In spite of his weak planning General Clark was awarded the Distinguished Service Cross for his brave conduct. Clark was frequently seen in the most forward positions encouraging his troops.