Patton graduated from West Point in 1909. He first saw action during the Pancho Villa Expedition in Mexico in 1916, the first US military action using motor vehicles. He joined the new US Tank Corps of the AEF in World War I. He commanded the U.S. tank school in France before being wounded in action. Between the wars, Patton was a key figure in developing the principles of armored warfare. Rising through the ranks, he commanded the U.S. 2nd Armored Division at the U.S. entry into World War II.