To ensure the rapid production of planes a naval aircraft factory was erected at the Philadelphia Navy Yard. The contract for its construction was signed in August, 1917, and in the following March, 228 days after the breaking of the ground, the first machine had been completed and was given its trial flight. And a few days later this machine and another which had followed it to completion and trial were on their way to Europe. In the meantime, in order to meet the expansion which was foreseen to be necessary in naval aviation plans, the naval aircraft building was greatly enlarged. Included in the extension was a huge assembly plant for the assembling of airplane parts separately built in a large number and variety of private manufacturing plants whose work for the aircraft factory was directed by its management. By this means team work was secured, resulting in quick deliveries and an ample supply of craft for both service and training purposes. By September of 1918 enough naval aircraft had been shipped overseas to meet the needs of its assembly bases there for several months. The big rubber plants which had almost ceased the manufacturing of balloons renewed and expanded that phase of their activities and balloon fields and schools were created or enlarged and newly equipped. The completion of the Liberty motor brought the later development of the flying boat, used especially for coastal patrol work. [Illustration: _By Permission of New York Times Co._ NAVAL GUN ON RAILWAY MOUNT] Candidates for flying commissions were sent to technical institutions for special courses and afterward to flying stations for instruction in flying. The most difficult part of the problem of seaplane construction was that of finding skilled workmen and personnel for their direction acquainted with the making of aircraft. The same difficulty handicapped the procuring of trained officers and enlisted men for work at the supply and repair stations, which were constantly busy with the assembling and upkeep of the machines. To meet this difficulty half a score or more of schools for naval aviation mechanics were established in different parts of the country, with a force of instructors, who volunteered for the work, composed of professors in technical schools and colleges. From these schools came the trained mechanics and ground officers who filled the roster of the Naval Aviation Service at the end of hostilities.