The Italian armistice and the mainland invasion

Why invade mainland Italy if the Italian government was already negotiating an armistice?

The invasion and armistice were coordinated to secure Italy's surrender and enable a rapid Allied advance, but the hoped-for breakthrough failed and the landings should have been farther north.

The exchange challenges the value of landing on the Italian mainland once the Italian government was ready to leave the war. The invasion began on 3 September 1943, the day the armistice was signed, and before its public announcement on 8 September. The landing was meant to help secure the surrender and let Allied armies advance rapidly before German forces consolidated. That surge did not happen, and the difficult south-to-north campaign consumed far more time and lives than planners hoped. In this assessment, the mainland invasion was a good idea poorly executed, while landings farther north to reinforce the Italians around Rome offered a stronger operational concept.