Then came two months in a ground school, of which there were eight located in as many universities and technical schools in different parts of the country, where the cadet, under military discipline, received practical and theoretical training in the study of motors, airplane construction and other elements of aviation. By means of long hours and close application the young men did as much work during the two months spent at these schools as they would ordinarily have covered during an academic year. The next step was training at a field for primary flying under the dual control system and practice in solo flying until the cadet could pass the requisite tests which permitted him to be graduated as a Reserve Military Aviator, with the rank of second lieutenant. Then he passed on to other fields where he was taught advanced flying, acrobatics, night flying, formation flying and aerial gunnery, and afterward to a specialized field where he qualified to be a pursuit pilot and fly and fight his own machine, or to be a bombing or an observation pilot, or to do reconnoissance or photographic work. At the close of hostilities fields for every specialty had been constructed and equipped and the system of training was receiving its final development in the establishment of brigades at a large flying center where the men were formed into squadrons, trained for work together and sent overseas as a flying unit. The signing of the armistice found one such great center, ranking among the largest plants the United States had constructed for the prosecution of the war, almost completed, its several coöperating fields able to handle over 7,000 men at a time and turn out a steady weekly installment of air squadrons, each with its eighteen flying officers, five ground officers and 150 service, supply, construction and repair men, trained, organized and ready for the final two or three weeks of experience at the flying fields overseas before being sent to the front.