The first condition is fulfilled by placing them at a safe distance, concealing them from the view of the defence if possible, and guarding them against attack, and the access of incendiaries, etc., by strict application of ordinary defensive tactics, and a most thorough system of interior guards. Powder depots, trains, etc., especially are guarded against the access of all unauthorized persons. The second condition, when railroad communication is used, is satisfied by making the park conform to the best-planned railroad terminals and freight-yards. A type arrangement is given in Plate IX, Fig. 85, in which switches from the main line give access to as many side-tracks, _a_, _b_, _c_, _d_, etc., and spurs, 1, 2, 3, etc., as may be needed. When practicable, these sidings should connect at each end with the main line in order to afford free ingress and egress from both directions. They should be placed at such distances apart as to allow loading-platforms and the desired room for sheds, piles of materials, etc., between them; large areas being left for light, and small for heavy, materials. The spurs, 1, 2, 3, etc., should preferably be short; but if long, should be connected by switches. A Υ, as indicated, is frequently convenient for reversing complete trains without uncoupling the cars, and is indispensable when a turn-table is not available. When the powder-depot is separated from the main park it is better to reach it by a special track branching from the main line at some distance from the park, so that the ammunition-trains will not pass through or near the latter. The sketch given is proposed as a type only, since the park may occupy one or both sides of the main line, be long and narrow, short and broad, regular or irregular in outline, as may best conform to the ground available. Standard-gauge roads will, when practicable, be laid between the main park and the smaller depots. When this is not feasible, narrow-gauge tram-roads will be used instead, and will also connect the smaller depots with the trenches and batteries. The portable tramways used by contractors are well fitted for use in the trenches. When the park is located upon navigable water a number of piers and wharves are occupied. They should be provided with derricks or cranes, and tracks and cars upon which materials may be loaded directly from the ships. The park may then be arranged on the general plan above indicated. The switches are so arranged as to allow empty cars to return to the wharves on a track different from that used by the loaded ones. In storing materials and supplies in the park care must be taken to place each class by itself, and to so pile them that they can be readily inventoried and inspected, and be removed or replaced without disturbing other piles. This requires the piles to be arranged in regular order, with unobstructed passages between them, and prohibits piling articles of different kinds or sizes on top of each other.