Jan. 1 to Apr. 1 to July 1 to Oct. 1 to Name of engine Mar. 31 June 30 Sept. 30 Nov. 8 Total Liberty 12, Army 122 1,493 4,116 4,093 9,824 Liberty 12, Navy 142 633 1,710 1,087 3,572 Hispano-Suiza 180 h. p. ... ... 185 284 469 IMPROVEMENT IN INSTRUMENTS AND ACCESSORIES Few facilities existed for the manufacture of many of the delicate instruments and intricate mechanisms going into the equipment of every battle-plane. The courage and determination with which these most difficult problems were met and solved will form one of the bright pages in the archives of American industry. One of the most important outgrowths of the research work which the war stimulated was the development of voice command in formation flying by means of wireless devices. The great significance of this invention will be appreciated when it is realized that the leader of a formation has heretofore been dependent on signals for conveying instructions to the individual units of the squadron. TRAINING OF PERSONNEL After the declaration of war the construction of training fields proceeded with such rapidity that the demand for training equipment greatly exceeded the output. Since the latter part of 1917, however, the supply of elementary training planes and engines has been more than sufficient to meet the demands, while the situation as regards certain types of planes for advanced training has greatly improved. Approximately 17,000 cadets were graduated from ground schools; 8,602 reserve military aviators were graduated from elementary training schools; and 4,028 aviators completed the course in advanced training provided in this country. Pending the provision of adequate equipment for specialized advanced training, the policy was adopted of sending students overseas for a short finishing course before going into action. The shortage of skilled mechanics with sufficient knowledge of aeroplanes and motors was met by the establishment of training schools from which over 14,000 mechanics were graduated. At the cessation of hostilities there were in training as aviators in the United States 6,528 men, of whom 22 per cent were in ground schools, 37 per cent in elementary schools, and 41 per cent in advanced training schools. The number of men in training as aviator mechanics was 2,154. FORCES AT THE FRONT Early in 1918 the first squadrons composed of American personnel provided with French planes appeared at the front. The number was increased as rapidly as equipment could be obtained. On September 30, the date of the latest available information, there were 32 squadrons at the front; of these 15 were pursuit, 13 observation, and 4 bombing. The first squadron equipped with American planes reached the front in the latter part of July.