During World War II, Marshall was instrumental in preparing the U.S. Army and Army Air Forces for the invasion of the European continent. Marshall wrote the document that would become the central strategy for all Allied operations in Europe. He initially scheduled Operation Overlord for April 1, 1943, but met with strong opposition from Winston Churchill, who convinced Roosevelt to commit troops to Allied invasion of Sicily for the invasion of Italy. Some authors think that World War II could have ended earlier if Marshall had had his way; others think that such an invasion would have meant utter failure.