"Will you explain just how it works?" asked Jack. I "Certainly. The periscope consists, as you may see, of a slender tubular shaft extending up through the conning tower of the submarine. Each submarine is equipped with a pair--thus if one is shot away the other can be put in immediate use. At the upper end of the shaft is a mirror lens. Upon this mirror lens is reflected the surrounding surface of the ocean. The image reflected there is carried down the tube to other lenses and then conveyed to enlarging binoculars. Now do you understand?" "Perfectly," replied Jack; "and now as to the manner in which a submarine fights. It is by torpedoes, as I understand it." "Exactly," replied the lieutenant, "and the torpedo is the most deadly, effective and, it may be also said, intelligent of modern warfare. One torpedo, striking the right kind of a blow, can destroy a battleship. The submarine has no other effective, weapon than the torpedo, which is delivered from a small tube. There is this advantage in favor of the battleship, however: the submarine is a slow craft. It is slower than the slowest battleship when it proceeds under water. When it gets to the surface its speed is doubled, but then it is an easy target for the guns of the threatened battleship and also for the swift torpedo boats and torpedo destroyers which are always thrown out as escorts when a submarine attack is anticipated. Some submarines are equipped with light rapid-firing guns, but these are of no more use in attacking on-water boats than would be a popgun. Do I make myself clear?" "Perfectly," said Jack. "It is indeed interesting," said Frank. "Can you tell us more?" The lieutenant continued: "Beyond these factors--the superior speed, the protection of torpedo boats and the weakness of the periscope--there has been no protection yet devised against the attack of a submarine." "But the torpedo nets--?" interrupted Frank. "There is of course," the lieutenant went on, "a crudely defensive measure called the torpedo net. These are meshes of strong steel which are dropped down from the side of the warship and are supposed to catch the torpedo before it hits the side of the ship." "Well, don't they?" asked Frank. "In theory," said the lieutenant, "the torpedo explodes within the net and the force of its attack is more or less diminished. As a matter of fact, however, torpedo nets are not dependable. Why, most of our submarines are equipped with a formidable device for cutting these nets. This device, in one form, resembles an enormous pair of sheers which cut through the nets like paper. In another form they are equipped with powerful tearing arms which drag the net away and expose the sides of the battleship to the deadly messenger from the torpedo tube. Am I tiring you?" "I should say not," replied both lads in one breath, and Frank added: "I don't just understand how a submarine sinks and rises."