3 September 1943
The new Italian government signed a secret armistice with the Allies. Immediately after, Operation Baytown, the invasion of the Italian mainland, was launched across the Strait of Messina, with British and Canadian troops of British XIII Corps landing at Reggio Calabria without opposition.
Having driven Axis troops out of the island of Sicily by 17 Aug 1943, the Allies launched Operation Avalanche, the invasion of mainland Italy. Given a choice of two landing sites, the opening of the Volturno River north of Naples or Salerno southeast of Naples, the latter was chosen as it had landing beaches favorable to invaders and it had nearby major roads and airfields that could be used by the Allies after a successful invasion. Operation Baytown and Operation Slapstick were launched to prepare for the main Operation Avalanche invasion, although the latter was actually commenced on the same day as Operation Avalanche.