Dugouts have become such a commonplace in the past four years that few, save the miners themselves, gave much thought to or had more than the haziest ideas of the time, skill, and labor required in their construction. Take yourself, for example. You have read about dugouts and seen pictures of dugouts and have probably had relatives or friends living in dugouts. How long, then, think you, would it take a force of skilled miners to complete a front-line dugout large enough to accommodate a half-platoon? (For your information I might explain that such a dugout is 35 feet long, 9 feet wide, and 6 feet high, with 17 feet of overhead cover.) Using all the men that could be employed, and working from nightfall until dawn, it would require at least three months to complete such a dugout. If in the rear area, where the men could be worked continuously in shifts, it could be completed in about thirty days. [Illustration: NEW TYPE OF SEARCH-LIGHT USED IN THE AMERICAN ARMY. The steel tower is collapsible and light and, being mounted on a motor-truck, is extremely mobile.] [Illustration: CAMOUFLAGING A DIVISIONAL HEADQUARTERS IN THE TOUL SECTOR. Constructing the screen. The screen as it appeared upon completion.] A recent and little-advertised development of trench warfare was the introduction of “mobile charges.” These consisted of packages of high explosive in ten, twenty, or thirty pound sizes, which were used by assaulting troops for destroying dugouts, much as depth bombs were used by the navy to destroy submarines. With the increasing use of mobile charges it became necessary to design dugouts which would be proof against them. In this work, which was carried on by the Mining School, extensive use was made of dogs, experiments having shown that explosions which will rupture the lung-tissues of a dog will similarly affect those of a human being. Thanks to the knowledge thus obtained at the cost of canine lives, a type of dugout construction was perfected which afforded the occupants comparative immunity from mobile charges and hand-grenades. An ingenious receptacle for this latter form of enemy visiting-card was the “bomb-pit,” which was a sort of small cistern, built at the foot of the dugout stairs, into which a hand-grenade would fall and explode harmlessly. Though it has no direct relation to the work of the American Mining School, I might mention, as an illustration of the part played by miners in the great conflict, that when the British in 1917 blew off the entire top of Messines Ridge prior to their assault on that position, 19 mines, containing a total of 950,000 pounds of ammonal—equivalent to 1,580,000 pounds of dynamite—were exploded simultaneously. A single one of these mines contained 95,000 pounds of ammonal and made a crater 186 feet wide and 125 feet deep. * * * * *