George Marshall directed the U.S. Army in the largest war in its history, building it from a tiny force to more than eight million. Before Japan’s attack on Pearl Harbor of December 7, 1941, Marshall led the effort to prepare the nation for war. Afterward, he helped direct the war effort and lead the United States and its allies to victory. Marshall became President Franklin Roosevelt’s leading military advisor and helped draft many of his memos on strategy and military matters.