1. From shrapnel bullets: 2-inch planks covered with 12 inches of earth. 2. From 3-inch shells: 4-inch planks supporting 4 feet of earth with a top layer of heavy stones to cause an early shell burst. [Illustration: PLATE 24.—Type of dugout.] 3. From howitzers of less than 6 inches caliber: 12-inch beams or logs covered with 8 feet of earth. 4. From the largest caliber guns: 15 to 25 feet of earth. The following table shows the penetration of the German S bullet at a range of 200 yards: _Inches_ Steel plate 3/8 Broken stone 6 Brickwork, cement and mortar 9 Brickwork, lime and mortar 14 Sandbags 24 Sand, loose 30 Hardwood, oak, etc. 38 Earth 50 Soft wood, poplar, etc. 58 Clay 60 Dry turf 80 In addition to the regular “dugouts” for the supports, the latest type trenches have squad dugouts just in rear of the bays of the fire trench. These provide shelter during bombardment for the members of the squad not actually required on duty in the trench bay. [Illustration: PLATE 24a.—Section of traversed type of fire trench showing entrance to squad dugout.] [Sidenote: Communications] The fire trench is connected with the cover for supports by a system of zigzag trenches having the profile shown in Plate 23. The arrangement is shown in Plate 1. [Sidenote: Trench Mortar Positions] Somewhere between the first line fire trench and the cover for the supports is a line of emplacements for the trench mortars. Plate 25 shows a profile of the emplacement. [Illustration: PLATE 25.—Profile of trench mortar emplacement.] The arrangement of the position is shown in Plate 1. These trench mortars are used to hurl charges of high explosives varying from 25 to 100 pounds into the enemy’s lines. They have a range of from 300 to 1,800 yards. [Illustration: PLATE 25a.—Trench mortar.] [Illustration: PLATE 25b.—Improvised catapult.] [Sidenote: Cover for Supports] At a variable distance to the rear of the first line fire trench is located the cover for supports, which is organized much in the same manner as the first line system of trenches and affords a second position in the system to fall back to in case of necessity. These trenches are provided with overhead cover and numerous dugouts for the protection of the men. [Sidenote: Machine Guns] At every available place throughout the defensive position machine guns are located, typical positions of which are shown in Plate 1. The typical types of cover are shown in Plates 26 and 27. Machine guns are a very potent factor in trench warfare. They are now being employed to a far greater extent than ever before, and the number is increasing on all the battle fronts as fast as they can be manufactured. The machine-gun positions are carefully concealed from the enemy, and fire is not opened until it is certain that it will be effective.