 Complete the following phrase:  In 1917, upon the United States entry into World War I, the first major U.S. aviation combat force was created when an Air Service was formed as part of the American Expeditionary Force AEF. Major General Mason Patrick commanded the Air Service of the AEF; his deputy was Brigadier General Billy Mitchell. These aviation units, some of which were trained in France, provided tactical support for the U.S. Army, especially during the Battle of Saint-Mihiel and the 