This carriage construction for the big guns required the closest kind of fine machine work and fittings where the brake or recuperator construction entered the problem, and the great plants built for this purpose of turning out carriages and recuperators were marvels for the rapidity of their construction, the speed with which they were equipped with new and intricate tools, and the quality of their output. Every mobile gun mount must be equipped with a shield of armor plate. The size of the artillery project may be read in the fact that our initial requirement for armor for the guns ran to a total of 15,000 tons to be produced as soon as it could be done. Now, we had no real source for getting armor in such large quantities, because the previous demands of our artillery construction had never called for it. The prewar manufacturers of artillery armor were three in number--the Simmons Manufacturing Co., of St. Louis; Thomas Disston & Sons, of Philadelphia; and the Crucible Steel Co. To meet the new demand two armor sources were developed--the Mosler Safe Co. plant of the Standard Ordnance Co. and the Universal Rolling Mill Co. The process of building this armor had been a closely guarded secret in the past, a fact entailing extended experiments in the new plants before satisfactory material could be obtained. The new artillery program required the manufacture of 120,000 wheels of various types and sizes for the mobile carriages. The Rock Island Arsenal and two commercial concerns prior to the war had been building artillery wheels in limited quantities. One completely new plant had to be erected for the manufacture of wheels, while seven existing factories were specially equipped for this work. We had to develop new sources of supply of oak and hickory and to erect dry kilns especially for the wheel project. The largest order for rubber tires in the history of the American rubber industry was placed as one relatively small phase of the artillery program, the order amounting to $4,250,000. Rubber tires on the wheels of all the heavier types of artillery carriages, so that the units might be drawn at good speed by motor vehicles, was essentially an American innovation. No tires of this size had ever been manufactured in this country. Consequently it was necessary for the firms who got the orders to build machinery especially designed for the purpose. With practically all of the manufacturers of the American metal-working industries clamoring for machine tools, and with some branches of the Government commandeering the machine-tool shops in whole sections of the country, it is evident that the necessity for the heavier types of machine tools required by the manufacturers of artillery material offered a weighty problem at the outset. In fact, the machine-tool supply was never adequate at any time, and the shortage of this machinery hampered and impeded to a great degree the speed of our artillery production.