It was in the spring of 1918 that the United States submarine X-111 was launched upon its adventurous career. The German commerce raiders had now reached the height of their effectiveness; almost daily they were taking their toll of luckless seamen and provision-laden steamers; and the United States government, in alarm that was never officially admitted, had resolved upon desperate measures. The result was the X-111. The first of a fleet of undersea craft, this vessel was constructed upon lines never before attempted. Not only was it exceedingly long (being about two hundred feet from stem to stern), but it was excessively narrow, and a man had to be short indeed to stand upright within it on its single deck without coming into contact with the arching ceiling. The ship, in fact, was nothing more nor less than a long pipe-like tube of reinforced steel, able to cleave the water at tremendous speed and ram and destroy any enemy by ramming it with its beak-like prow. But this was only its slightest point of novelty. At both ends and at several points along the sides it was equipped with water-piercing searchlights of a power never before known (the creation of Walter Tamrock, the Kansas inventor who lost his life in the war); and it was provided with a series of air-tight and water-proof compartments, any one of which might be pierced without seriously injuring the vessel as a whole. Hence the X-111 was generally known as unsinkable, and upon it the American officials fastened their hopes of abating the nuisance of the enemy “U-boat.” The sinking of this “unsinkable” vessel is now of course a matter of history. Close observers of naval events will recall how, in May, 1918, the newspapers reported the disappearance of another United States submarine. All that was known with certainty was, that the ship had been commissioned to the danger zone; that it had failed to return to its base at the expected time, and that the passing days brought no news of it; that wireless messages and searching expeditions alike proved unavailing, and that it was two months before the only clue as to its fate was found. Then it was that a British destroyer, on scout duty in the North Sea, picked up a drifting life preserver bearing the imprint “X-111.” For strategic reasons, this fact was not divulged until much later, and for strategic reasons it was not made known that the missing submarine was of a new and previously untried type; but the mystery of the X-111’s disappearance weighed heavily upon the minds of naval officials, and secretly they resolved upon immediate and exhaustive investigation. All in vain. Not a trace of the lost ship or of the thirty-nine members of its crew could be found; not a scrap of the usual drifting flotsam or wreckage could be picked up anywhere on the sea; and at last it was admitted in despair that the waters would perhaps guard their secret forever.