The actual building of the airplanes gave a striking example of the value of previous experience, either direct or of a kindred nature, in the quantity production of an article. What airplanes we had built in the United States--and the number was small, being less than 800 in the 12 months prior to April, 1917--had been entirely of the training type. These had been produced principally for foreign governments. But this slight manufacture gave us a nucleus of skill and equipment that we were able to expand to meet our own training needs almost as rapidly as fields could be equipped and student aviators enlisted. The training-plane program can be called a success, as the final production figures show. Of the 11,754 airplanes actually turned out by American factories, 8,567 were training machines. This was close to the 10,000 mark set as our ambition in June, 1917. There are two types of training planes--those used in the primary instruction of students and those in the advanced teaching, the latter approaching the service planes in type. The primary plane carries the student and the instructor. Each occupant of the fuselage has before him a full set of controls which are interconnected so that the instructor at will can do the flying himself, or correct the student's false moves, or allow the student to take complete charge of the machine. These primary planes fly at the relatively slow speed of 75 miles per hour on the average and require engines so reliable that they need little attention. For our training planes we adopted the Curtiss JN-4, with the Curtiss OX-5 engine, and as a supplementary equipment the Standard Aero Corporation's J-1 plane, with the Hall-Scott A-7-A engine. Both of these planes and both engines had been previously manufactured here. The Curtiss equipment, which was the standard at our training camps, gave complete satisfaction. The J-1 plane was later withdrawn from use, partly because the plane itself was not liked, partly because of the vibration resulting from this Hall-Scott engine, it having only four cylinders, and partly because of the uncertainty of the engine in cold weather. [Illustration: CURTISS JN4-D, USED AS A PRIMARY TRAINING MACHINE. ENGINE, CURTISS OX-5. This machine has a dual control and is used solely for training purposes.] [Illustration: V. E. 7. EQUIPPED WITH 180-HORSEPOWER HISPANO-SUIZA ENGINE. An American designed training plane.] It was evident that at the start we must turn our entire manufacturing capacity to the production of training planes, since we would need these first in any event, and we were not yet equipped with the knowledge to enable us to make intelligent selections of service types.