Though I have described at some length the use of silhouettes and papier-maché heads because they are picturesque and interesting phases of modern war, it should be borne in mind that they were designed to meet exceptional conditions, that they were used infrequently, and that they were in no sense typical of the enormously important work of the Camouflage Service. * * * * * In the foregoing pages I have sketched the multitudinous activities of the Engineers only in the barest outline. To attempt to compress the story of their achievements into the limits of a single chapter would be absurd, so I have dwelt only on the most picturesque and unusual phases of their work—the high spots, as it were. There is much that I have left unsaid, not because it is not worth saying, but because I have no space in which to set it down. The stories which I have had, perforce, to leave untold would in themselves fill a volume. Among their other accomplishments the Engineers designed a portable steel bridge, made up in sections so that it could be transported on trucks, and so designed that it could be bolted together, which could sustain a load of thirty tons over a span of ninety feet. These bridges were used all along the fighting front, as our forces advanced, to replace the bridges destroyed by the retreating Germans. They had under construction, when the war ended, a raft designed for the transportation of the heaviest pieces of mobile artillery in existence—by means of which, had necessity required it, we could have ferried our giant howitzers across the Rhine. The portable floating foot-bridges—passarelles—which our troops used in crossing the Meuse and the adjacent canals under fire were invented by an officer of Engineers. The Engineers threw one of them across the Canal de l’Est, near Dun-sur-Meuse, under a shell and machine-gun fire so heavy that it was twenty-six hours before the infantry could cross it. The Engineers have invented a very ingenious and remarkable device whereby search-lights can be operated from a distance, thus making it possible for an officer to control a battery of scattered search-lights just as the man in a signal-tower controls, by means of levers, the switches in a railway yard. The corps has perfected a blasting machine for demolition work which destroyed ruins faster than the Huns could make them. Military operations are absolutely dependent upon maps and plenty of them. The Engineers met the demand by erecting and operating in France a larger map-producing plant than was possessed by France herself or any of the Allies. In order to provide a more rapid means of obtaining topographical information, Major James W. Bagley, of the Engineers, invented an aerial cartograph or mapping camera, which takes three pictures at a time from an airplane, mapping a strip of territory three and a half miles wide at 5,000 feet elevation, the series of pictures thus taken forming a mosaic