Of this total, 9,834 were high-compression, or army type, and 3,572 low-compression, or navy type, the latter being used in seaplanes and large night bombers.
In addition to those installed in planes, about 3,500 Liberty engines were shipped overseas, to be used as spares and for delivery to the Allies.
Other types of service engines, including the Hispano-Suiza 300 h. p., the Bugatti, and the Liberty 8-cylinder, were under development when hostilities ceased. The Hispano-Suiza 180 h. p. had already reached quantity production. Nearly 500 engines of this type were produced, about half of which were shipped to France and England for use in foreign-built pursuit planes.
Table 22 gives a résumé of the production of service engines by quarterly periods:
Table 22.—Production of service engines in 1918.
| Name of engine | Jan. 1 to Mar. 31 | Apr. 1 to, June 30 | July 1 to Sept.30 | Oct. 1 to 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