Practically all field artillery was of the horse-drawn type previous to our entry into the war, but with the evolution and perfection of the heavier siege artillery, 5-ton, 10-ton, and even heavier, traction engines were brought into play as means of motive power for the big guns and howitzers, with such success that the horse in the field artillery operations was being supplanted to a large degree by mechanical power. Strictly speaking, the foundation for this departure had been laid before 1917, in the Mexican campaign of 1916 and in experiments that had been conducted at the Rock Island Arsenal. Insufficiency of funds, however, had prevented the experiments from being either thorough or extensive. A consideration of the difficulties that vehicles of all sorts had to contend with in the battle areas of Europe made it evident at the outset that two general types of motor carriers would be required by the Army so far as ordnance was concerned--one type for far-advanced work, for hauling artillery over the worst possible kind of shell-torn and water-soaked earth, and the other for bringing up ammunition, supplies, equipment for repairs and the like in less advanced zones and areas, but over roads and country that had been cut and hacked and made almost impassible by the activities of the contending forces. TRUCKS. The standard four-wheel-drive commercial trucks, modified to meet the special needs of the service, were adopted immediately after war began, while experimental work was put under way to develop a standard type that would set this country far in advance of all others in this line of activity. A total of 30,072 of the four-wheel-drive trucks was ordered, and before the armistice 12,498 of this number had been completed, while 23,499 had been turned out by the 31st of January, 1919. In round numbers, 25,000 of these trucks were to be equipped with bodies for the hauling of ammunition, and the balance with special bodies and equipment suitable for artillery supply and repair, for repair of equipment, and for heavy mobile ordnance. [Illustration: ARTILLERY SUPPLY TRUCK ON F. W. D. CHASSIS. This truck was designed with special bodies and loads for varied classes of artillery supply, and the bodies could be mounted on either Nash or F. W. D. chassis.] [Illustration: ARTILLERY REPAIR TRUCK ON F. W. D. CHASSIS. This is another special body equipped with suitable machinery and tools for minor repairs and capable of being mounted on either F. W. D. or Nash four-wheel-drive chassis.] [Illustration: AMMUNITION TRUCK MOUNTED ON STANDARD ORDNANCE FOUR WHEEL DRIVE TRACTOR. This is the vehicle, designed by the Ordnance Department and civilian experts, that was intended to supersede both the Nash and the F. W. D. and become the standard Army wheeled tractor. It is shown here with standard ammunition body mounted thereon.] [Illustration: ORDNANCE EQUIPMENT REPAIR TRUCK ON F. W. D. CHASSIS.