Between 1910 and 1917 a number of aviation units were organized in the National Guard. While only the 1st Aero Company, New York National Guard, was federally recognized, a numbered of other states had aircraft, and some 100 National Guardsmen took flight training. But when the U.S. entered World War I, the War Department decided not mobilize National Guard aviation units, and so National Guard aviators entered Federal service as individuals. First Lieutenant Reed M. Chambers, a former Tennessee Guardsman, was assigned to the 94th Aero Squadron along with Eddie Rickenbacker, who would become the leading American ace of the war. The squadron arrived in France on March 4, 1918, and one month later became the second American flying unit to see action, credited with two kills on its first day in combat. The 94th participated in the Chateau-Thierry and Aisne-Marne campaigns, and then in the Meuse-Argonne offensive, the largest U.S. operation of the war. On October 22, 1918, 1st Lieutenant Chambers, flying his Spad, shot down two Fokker D-7s to become the first national Guard ace of the war. Chambers was awarded the Distinguished Service Cross with an oak leaf cluster for extraordinary heroism in aerial combat and ended the war with five downed German plans to his credit. After the war, combat-experienced aviators such as Reed Chambers returned home and organized 18 National Guard observation squadrons, which became the nucleus of today's Air National Guard.