It might also be stated at this point, too, that two special types of passenger motor vehicles were designed and built. One of these was for staff observation and the other for reconnaissance. Nearly all of the total of 2,250 that were ordered of these two types were completed by mid-December, 1918, delivery of them having started in the month of April, 1918. CATERPILLAR TRACTORS. It was found after a comprehensive study of the needs of the various branches of ordnance and the requirement of the big guns that five sizes of caterpillar tractors would be required--of capacities of 2½ tons, 5 tons, 10 tons, 15 tons, and 20 tons. Commercial types of machines of the 15-ton and 20-ton sort, with only slight alterations, were found to be suitable, but special designs were made for those of 2½-ton, 5-ton, and 10-ton capacity. Our experience in Mexico and the experiments at the Rock Island Arsenal had taught us the need of the special designs of machines of those sizes. In all, 24,791 of these five types of caterpillar tractors were ordered. The 5-ton machine reached production in the summer of 1918 and the 2½-ton machine in the fall. By the end of the following January, 5,940 of the tractors had been delivered. Manufacturers who had orders for the caterpillar tractors were: Holt Manufacturing Co., Peoria, Ill. Chandler Motor Car Co., Cleveland, Ohio. Reo Motor Car Co., Lansing, Mich. Maxwell Motor Car Co., Detroit, Mich. Federal Motor Truck Co., Detroit, Mich. Interstate Motor Co., Indianapolis, Ind. Throughout the production of tractors during the war period there was continuous and persistent experimentation, and satisfactory solutions of many of the problems were being reached at the time of the signing of the armistice. Self-propelled caterpillar gun mounts were the subject of the most important of these experiments. The self-propelled caterpillar gun mounts differ from the ordinary caterpillar tractors in that they have the guns mounted directly on them, the guns forming an integral part of the entire machine. Six types of these were being developed, and 270 had been ordered when the armistice came. A 2½-ton tractor mounting a 75-millimeter gun and a 5-ton tractor containing a gun of the same size were far along the road to success in their first state of development. Development of caterpillar cargo carriers or caissons for bearing supplies over any sort of terrain, no matter how rough the going might be and regardless of whether there were roads or not, was so far along the pathway of success that two sizes were about to go into production on November 11. A 2½-ton ammunition trailer, a 2-ton 11-inch trench mortar trailer, and a 4.7-inch antiaircraft gun trailer were also in development, but not in production, at the time of the signing of the armistice.