Then, it ceased to be quite so one-sided a game when merchantmen began to carry guns. That made it necessary for the submarine commander to creep up on his victims stealthily, and depend upon his torpedoes. He had to get within a thousand yards of the ship and preferably within five hundred yards, in order to be sure of hitting it. If the ship could travel faster than he could, he had to do this without betraying his presence. But ship-captains soon learned that their safety lay in zig-zagging. When _Herr Kommandant_ reached the point from which he had planned to attack, he would raise his telescopic periscope out of the water, expecting to see his victim within good torpedo range, only to find it sailing safely on another tack. Again, he would have to take observations and make another try, probably with no better luck. It was a game of hide-and-seek in which the merchant ship had a good chance of making its escape, particularly when blotches of camouflage paint made it difficult for him to get the range, as described in Chapter XI. [Illustration: Courtesy of the Submarine Defense Association FIG. 19. How a ship hid behind smoke produced on its own stern, with different directions of wind] Slower ships could be attacked without all this manoeuvering, provided the submarine's guns outranged those of the ship. And so U-boats were provided with larger and larger guns, which made it possible for them to stand off and pound the merchantmen while out of reach of the vessel's guns. But ships found a way of hiding on the surface of the sea. A vessel would spout forth volumes of dense black smoke which would obliterate it from view. (See Fig. 19.) If the wind was quartering, the ship would change its course and dodge behind the sheltering pall of smoke. Not only was the smoke produced on the vessel itself, but smoke-boxes were cast overboard to form a screen behind the vessel. These smoke-boxes contained a mixture of coal-tar and phosphorus and other chemicals which would produce incomplete combustion. They were ignited by the rubbing of a phosphorus compound on a priming-composition, and then cast adrift to pour out dense volumes of heavy smoke. (See Fig. 20.) Behind this screen, the ship could dodge and zig-zag and if her speed were greater than that of the submarine, her chances of escape were very good. [Illustration: Courtesy of the Submarine Defense Association FIG. 20. How a ship hid behind a screen of smoke produced by throwing smoke-boxes overboard] Another annoyance that _Herr Kommandant_ experienced was, when he lifted his periscopic eye above water, to find it so smeared with a sticky substance that he could not see. His foes had strewn the water with tar-oil that had spread in a thin film over a surface miles in extent. This blinded him at first, but before long he was equipped with a jet for washing off the periscope glass and that little annoyance was overcome.