The periscope of a submarine that is running awash can be raised about fifteen feet above the water, which means that the horizon as viewed from that elevation is about six miles away, and if you draw a circle with a six-mile radius on the map of the Atlantic, you will find that it is a mere speck in the ocean; but a U-boat commander could see objects that lay far beyond his horizon because he was searching for objects which towered many feet above the water. The smoke-stacks of some vessels rise a hundred feet above the water-line, and the masts reach up to much greater altitudes. Aside from this, in the early days of the war steamers burned soft coal and their funnels belched forth huge columns of smoke which was visible from twenty to thirty miles away. When this was realized, efforts were made to cut down the superstructure of a ship as much as possible. Some vessels had their stacks cut down almost to the deck-line, and air-pumps were installed to furnish the draft necessary to keep their furnaces going. They had no masts except for slender iron pipes which could be folded down against the deck and could be erected at a moment's notice, to carry the aërials of the wireless system. Over the ship from stem to stern was stretched, a cable, familiarly known as a "clothes-line," upon which were laid strips of canvas that completely covered the superstructure of the ship. These boats lay so low that they could not be seen at any great distance, and it was difficult for the U-boats to find them. They were slow boats; too slow to run away from a modern submarine, but because of their lowly structure, they managed to elude the German U-boats. When they were seen, the U-boat commanders were afraid of them. They were suspicious of anything that looked out of the ordinary, and preferred to let the "clothes-line ships" go. [Illustration: (C) Committee on Public Information From Western Newspaper Union Camouflaged Headquarters of the American 26th Division in France] THE BRITISH MYSTERY SHIPS