The first two motor-truck units proved so extremely efficient that the organization of others was begun, and by June 30 there had been formed fifteen companies in all. The personnel of these early motor-transport companies was civilian, the drivers and repair men being provided by the factories which supplied the trucks, but it quickly became apparent that the employment of civilians would not prove satisfactory because of their lack of discipline and the consequent difficulty of keeping them under control, the officers not knowing how to handle civilians. So, whenever possible, enlisted men who had had experience with motor vehicles or who possessed some mechanical aptitude were transferred to the truck companies to replace the civilians, the latter remaining on to give instruction in driving and maintenance. Maintenance is, I might add, perhaps the most important factor in the successful operation of motor vehicles, for broken-down cars must be repaired, worn parts must be replaced, and the vehicles must frequently be overhauled. In order to maintain in a state of efficiency the truck trains operating in Mexico, it was found necessary, therefore, to build repair-shops and to organize repair crews. Though the personnel of these shops, like the drivers, was at first largely civilian, it, too, was gradually replaced by enlisted men, so it may be said that by the opening of 1917 motor transportation had become a recognized branch of the military establishment, although it was not until some time after declaration of war that it was authorized for the army.