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.
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.
Plate 24a.—Section of traversed type of fire trench showing entrance to squad dugout.
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