"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.