The delivery of seaplanes for training purposes has been sufficient to more than meet the requirements. The training of personnel and providing of stations and equipment to carry out this training had expanded sufficiently so that the output of pilots, observers, mechanicians, and men trained in special branches was keeping abreast or ahead of requirements. The navy aircraft factory produced aircraft valued at $5,435,000 up to the time the armistice was signed. It had completed, ready for shipment, 183 twin-engine flying-boats, at an average cost of $25,000. It had also produced 4 experimental Liberty-engine seaplanes, carrying the Davis non-recoil gun, at a cost of $40,000 each, and 50 sets of twin-engine flying-boats’ spare parts worth $10,000 per set. In addition considerable minor experimental work and overhauling of machines from other stations was done. The main factory at Philadelphia had a capacity of 50 boats, and could turn out an average of 5 machines a day when the armistice was signed. On October 1, 1917, the first mechanic was hired at the navy aircraft factory. On November 1, 1918, there were 3,642 men and women employed in building flying-boats for the navy. About 1,500 Liberty engines were delivered to the navy and assigned to naval air-stations in this country and abroad. Since the number of Liberty engines produced were too small for the needs of the army alone, it had been necessary for the navy to purchase others, to the number of about 700, which were utilized while awaiting a full supply of Liberty engines. In addition to these a large number of engines of less power were bought for use in training-planes, all of which were distributed to the flying-schools. One of the very important duties devolving on the Bureau of Steam Engineering was the equipment and maintenance of stations for the generation of hydrogen for use in airships. A number of stations were established, and a full equipment of hydrogen cylinders provided, so that any calls might be promptly met. CHAPTER IX THE DEVELOPMENT OF THE AERO MAIL FIRST MAIL CARRIED BY AIRCRAFT—NEW YORK-PHILADELPHIA-WASHINGTON SERVICE—NEW YORK-CLEVELAND-CHICAGO SERVICE—FOREIGN AERO MAIL ROUTES As soon as the aeroplane demonstrated that it could travel at least twice as fast as the fastest express-train, even when going in the same direction, and that in addition it could traverse mountains, rivers, forests, swamps in a straight line, its possibilities as a mail-carrier were immediately realized, and steps were taken in most countries to establish aero mail routes.