The machine guns of a fortress should be divided into two classes--the stationary and the mobile guns. To the former will be allotted the defence of distinct portions of the permanent works, and they will be provided with cone and parapet mountings,[39] the former being fixed and the latter capable of being moved within the work to which it is allotted. The mobile guns should be mounted on a light tripod and carried in a low-wheeled handcart, or they may be mounted on a very light two-wheeled carriage capable of being drawn by one man and having wheels of small track, which can move over the narrowest roads in the fortress. These mobile guns should not be allotted to any particular work, but to the garrison other than those within the forts, for use in repelling assaults and making counter-attacks. We will deal first with the stationary machine guns. It will not be necessary to provide a machine gun for each cone mounting, as the guns can be easily carried from one cone to another as required. Shields should be used with all stationary mountings, but must be detachable, and should not be placed in position until required, as they indicate the situation of the gun and are easily destroyed by artillery. The positions for machine-gun mountings in a fort must depend on the size and construction of the work, the nature of the outer defences, and particularly on the supporting works in the immediate vicinity. Positions commanding the glacis and the entanglements, on salients of works and enfilading ditches, and any dead ground where the enemy may effect a lodgment, are suitable. Counterscarp galleries at the angles of works flanking the ditch should invariably have machine-gun positions, with a special loophole, long and shallow, to enable them to sweep a wide area with fire.