In the present European war, for the first time in the world's history, the submarine, as is also the case with the airplane, has taken an important active part, and has become a weapon of unlimited value. We have seen that even as early as the war of the American Revolution the submarine was utilized, but up to modern days the submarine had never been a really significant or consequential factor in naval warfare; its use had been previously but sporadic and experimental. In the wars of the past it had no bearing upon the destinies of nations or the outcome of naval battles. To-day the situation is very different: the submarine has been called into action as a weapon of primary value and is producing tremendous results. In the conflict in which we are now engaged the destructive capabilities of the submarine have been made use of, for the most part, in the work of commerce destruction and in the task of hampering communication by sea. It has not taken a great deal of active part in actual naval battles, although on some occasions its presence has been severely felt by the fleets of its enemies. But the submarine has been an important factor in naval warfare by reason of the fact that its very presence and the possibility of its use have checked the actions of belligerent fleets of battleships in no inconsiderable way. In writing of this I am reminded of the fact that a short time ago I was introduced to a pleasant-faced, motherly old lady who, when she learned that I was an inventor of submarine boats, exclaimed, "Why! I should not think you could sleep nights from thinking of all those poor people who have been drowned by the U-boats!"