But the physicist had barely rolled up his sleeves and got into the fray when the armistice was signed which put an end to the shams as well as to the realities of the great war. While the work of camouflage was not completed, we owe an inestimable debt to the men who knew how to fake scenery and to their learned associates who count the wave lengths of light, and although their trade was a trade of deception and shams, there was no sham about the service they rendered. MAKING SHIPS VISIBLE While in war safety lies in invisibility, in peace the reverse is true. Now that the war is over, it may seem that the work of the camoufleurs can find no useful application; but it was impossible to learn how to make objects invisible without also learning how to make them conspicuously visible. As a consequence, we know now how to paint a ship so that it will show up more clearly in foggy weather, thereby reducing the danger of collision. We know, too, how to paint light-ships, buoys, etc., so that they will be much more conspicuous and better guides to mariners, and how to color railroad signals and road signs so that they will be more easily seen by locomotive engineers and automobile drivers. CHAPTER XII SUBMARINES It was an American invention that dragged America into the war--an American invention in the hands of barbarians and put to unspeakably barbarous use. After seeing how the Huns used the submarine we are not so sure that we can take much pride in its invention. But if any blame attaches to us for developing the submarine, we made amends by the way in which we fought the German U-boat and put an end to German frightfulness on the sea. Of course, the credit for Germany's defeat is not for a moment claimed by Americans alone, but it must be admitted that we played an important part in overcoming the menace of the U-boat. There is no question that the submarine was an American invention. To be sure, we can look into ancient books and find suggestions for navigating under the surface of the sea, but the first man who did actually build a successful submarine was David Bushnell, back in the Revolutionary War. After him came Robert Fulton, who carried the invention farther. He built and operated a submarine for the French Government, and, in more recent years, the submarine became a practical vessel of war in the hands of John P. Holland and Simon Lake, both Americans. However, we are not interested, just now, in the history of the submarine, but rather in the development of this craft during the recent war.