If invisible casemates can be constructed this practice is good. The best method is, however, to prepare several emplacements, properly camouflaged, with a deep dugout near at hand for the protection of the M. G. and its crew. This shelter must be located at such a point that the M. G. can be quickly brought out to any one of its emplacements when the attack develops. These emplacements usually are simple pits located in front of the trench and connected with the dugout by a gallery. When emplacements are destroyed by hostile artillery fire, or when they are not possible, machine guns are pushed into shell holes or operated on the open ground. Shell holes out in front give the best service as emplacements for a daring M. G. crew. The French success at Verdun depended to a great extent upon the judicious use of shell holes for M. G. flanking fire. (_b_) Machine guns are not only located in the first line, but are disposed throughout the interior of the position. The hostile artillery may entirely destroy the first line of defenses, but the proper disposition of machine guns for flanking fire in the interior lines will prevent the enemy’s progress after penetrating the position. Machine guns are so located in the position as to cover all the space between the different lines with flanking fire. Usually three pickets define the sector to be covered by any one M. G., one at the M. G. and two limiting its sector of fire. In a sector, ⅓ of the machine guns are located in, or near the first line, ⅓ is disposed of in the support line or in the redoubt. The last ⅓ is assigned to the third line. In each line machine guns are under the command of the chief of the area. As a general rule, in the first line, automatic-machine rifles, because of their mobility, are used instead of machine guns. Standing orders are, that M. G. crews will never surrender, but fight to the last man. Often the tenacity of a M. G. crew has permitted the retaking of an area otherwise lost. =Trench Mortars.= In each sector there are located a certain number of trench mortars. These are efficient weapons, but must be used with care, because they will nearly always draw concentrated artillery fire. They are used for the destruction of special points in the enemy’s lines that the artillery cannot reach. They are employed in the preparation for an offensive against the enemy’s first line, either for an attack or for a raid. They are used for reply fire against enemy’s trench mortars. They participate in establishing barrages. The efficiency of trench mortars cannot be overestimated, but at the same time, great precaution must be taken in their use and concealment. The personnel required to serve the light trench mortars are taken from the garrison of the sector and belong to a special headquarters unit, a platoon of bombardiers.