The boys looked long at this strange mechanical eye. Shaped like a small pipe, it ran up from the conning tower and protruded above the vessel. A large lens at the top turned off as does an elbow in a stove pipe. This portion, when necessary, moved in all directions. When raised to its maximum height everything within a radius of ten miles is reflected in it.
"The shaft can be lowered to within a few inches of the top of the water," the lieutenant explained, "thus guarding against the danger of being hit. The officer in the conning tower peers into the binoculars and sees just what the periscope sees."
"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.