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 Lieutenant General Mark Clark's U.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).