In all, 53 new plants for making explosives and propellants and for loading these were undertaken at a cost of approximately $360,000,000. When the armistice was signed a very large part of this construction work had been completed and was in an efficient state of operation. How creditably this reflects upon America can be understood when it is made plain that in addition to the development of production there was also to be worked out the very intricate question of design, not only of the plants themselves but also of their products, which required an exceptional degree of technical skill and thorough control. Prior to our entry into the war the Ordnance Department had depended upon ammonium picrate, known in the Army vernacular as explosive "D," as a bursting charge for our high-explosive shell. During the progress of the European conflict the British had developed an explosive they called amatol, which is a mixture of trinitrotoluol--T. N. T.--and ammonium nitrate. As this had proved to be entirely satisfactory in actual service on European battle fields, and as ammonium nitrate could be produced here in large quantities, we adopted it. The Ordnance Department eventually put into effect a standard policy for the use of high explosives. Every effort was being made to conserve the supply of T. N. T., and consequently this explosive was specified for the shell of smaller calibers only. The standard filling scheme was as follows: T. N. T. for shell between and including the calibers of 75-millimeter and 4.7-inch; amatol for shell of calibers between 4.7-inch and 9.2-inch, including the latter; ammonium picrate, or explosive D, for shell of 10-inch caliber and higher. While these were the standards the scheme was not always followed rigidly. As a matter of fact amatol was loaded into shell of all sizes and so was T. N. T., although explosive D was never used in shell smaller than those for the 10-inch guns. These departures from standard practice were due to the necessity for keeping certain plants in production and to other special causes and exceptional circumstances. Production of large quantities of T. N. T. and ammonium nitrate was the first big problem to be solved by the high-explosives section of the Ordnance Department. All the work of the explosives section can be subdivided under four group heads--raw materials, propellants, high explosives, and loading. RAW MATERIALS. The first steps taken in the endeavor to meet the need for raw materials were to increase greatly the available means for obtaining toluol, phenol, caustic soda, sodium nitrate, sulphuric and nitric acids, ammonia liquor or aqua ammonia, and to attempt to provide a substitute for cellulose in case a shortage of cotton should render its use necessary.