Operation Avalanche and the Italian mainland. The Allied invasion of Sicily in July 1943, codenamed Operation Husky, was highly successful, although many of the Axis forces there were allowed to avoid capture and escape to the mainland. More importantly a "coup" deposed Benito Mussolini as head of the Italian government, which then began approaching the Allies to make peace. It was believed a quick invasion of Italy might hasten an Italian surrender and produce quick military victories over the German troops that would now be trapped fighting in a hostile country. However, Italian (and more so German) resistance proved relatively strong, and
Operation Avalanche tie down German forces, keeping them away from the planned invasion of Normandy – Operation Overlord. However, General George Marshall and much of the American staff wanted to undertake no operations that might delay the Normandy invasion. When it became clear that Operation Overlord could not be undertaken in 1943, it was agreed forces in North Africa should be used to invade Sicily, with no commitment made to any follow-up operations. Joint Allied Forces Headquarters AFHQ were operationally responsible for all Allied land forces in the Mediterranean theatre and it was they who planned and commanded the invasion of Sicily