“What do you mean?” his chief asked curiously. “It’s as plain as the nose on your face,” explained the youngster. “The Boche knows jolly well that if he walked across that open ground his tracks would show up in our air photos. So when he wants to get up to his battery he gets a couple of wooden biscuit-box covers and ties strings to them. He stands on one cover and throws the other ahead of him, then stands on that and drags up the first cover by means of the string and repeats the operation. Deuced clever of the beggars, I call it.” And, as subsequent events proved, the intelligence officer was right in his deduction. That was precisely what the Germans had done. By far the most important work of the Camouflage Corps was the construction of “flat-tops” and “false contours.” A flat-top, I should perhaps explain, is a screen for concealing a gun from enemy observation. It consists of a fish-net, usually 37 feet square, into the mesh of which are woven and knotted narrow strips of burlap of colors to blend with the vegetation of the region where the flat-top is to be used. The interwoven burlap becomes gradually thinner as the edges of the net are approached, so that no sharply defined shadow may be cast. Every piece of artillery, large and small, in the A. E. F. had its own flat-top, which accompanied the gun everywhere, being stretched above it, like a canopy, when the piece was in action, at other times being rolled up and carried on the limber. A somewhat similar device was also provided for the concealment of machine-guns. It resembled one of those huge umbrellas used in summer on delivery-wagons, and, like an umbrella, it could be quickly raised or lowered. It was the intention of the Camouflage Corps, had the war continued, to provide one for every machine-gun.