Allied invasion of Italy Allied invasion of Italy The Allied invasion of Italy was the Allied amphibious landing on mainland Italy that took place on 3 September 1943 during the early stages of 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 Fifth Army and General Bernard Montgomery's British Eighth Army) and followed the successful invasion of Sicily. The main invasion force landed around Salerno on 9 September on the western coast in Operation Avalanche, while two supporting operations took place in Calabria (Operation Baytown) and Taranto (Operation Slapstick).
Operation Avalanche the Allied armies a grinding and attritional slog against skillful, determined and well prepared defenses in terrain and weather conditions which favoured defense and hampered the Allied advantages in mechanised equipment and air superiority. It took until mid-January 1944 to fight through the Volturno, Barbara and Bernhardt lines to reach the Gustav Line, the backbone of the Winter Line defenses, setting the scene for the four Battles of Monte Cassino which took place between January and May 1944. Operation Avalanche Operation Avalanche was the codename for the Allied landings near the port of Salerno, executed on 9 September 1943, part