If the mining officer was convinced that the enemy was driving a gallery for the purpose of putting a mine under his position, two courses of action would be open to him. He could remain on the defensive and check the enemy’s advance by the use of “camouflets,” this being the name applied to explosive charges which expend their force laterally, thus destroying the enemy’s gallery without causing a crater; or he could resort to strategy and engage the enemy’s attention at one point by exploding camouflets or by working noisily, and under cover of this diversion drive a fighting gallery toward his flank elsewhere. If, instead of being content to remain on the defensive, the officer in charge of mining operations decided to assume the offensive, he would engage the enemy’s attention at one point, either by exploding camouflets or by working noisily, and at the same time drive a fighting gallery toward his adversary’s flank. In this latter case the most profound silence had, of course, to be enforced in the fighting branch if the enemy’s geophones were not to give warning of its approach. No talking was permitted, the men wore felt-soled shoes and worked with trowels instead of picks, and the earth was carried out in cars with rubber tires. So silently were the operations in the fighting branches conducted that they would frequently break into the enemy galleries without the slightest warning, whereupon would ensue a struggle fought scores of feet beneath the surface of the earth, by combatants armed with picks, pistols, bombs, and knives, and illuminated only by flickering miners’ lamps—a battle so weird and strange in its character and setting that it seemed like the creation of a motion-picture writer’s brain. One of the essentials for the success of a mining operation is the concealment of the spoil—_i. e._, the excavated earth—which, if piled in a heap at the entrance to the workings, would almost certainly be photographed by aerial observers, thus informing the enemy, as unmistakably as though it were announced on a placard, that a mining gallery was being driven. The French, in order to hide the spoil from their mining operations, conceived the ingenious plan of digging a shallow trench, usually only a few inches deep, and lining it with black paper, so that when photographed from an airplane it produced the effect of the black shadow cast by a trench of customary depth. They would then distribute the spoil from their subterranean galleries along the sides of this false trench, so that it appeared in the photograph to have been thrown up from it. * * * * *