Now, while a U-boat is a submarine, all submarines are not U-boats; for the word submarine means any and everything that lives, is done, or works beneath the surface of the sea. Thus, a fish is a submarine, and so is a boy while he is under water—though his clothes may be on the shore.
How the Submarine Came to Be.—Yes, the fish of the Paleozoic[4] era, see [Fig. 1], was the earliest submarine, in that it moved in and through the water under its own power, and that was millions of years before the human race and the monkey tribe branched off from a common ancestor.
FIG. 1. A PALEOZOIC SUBMARINE. IT WAS THE FIRST FISH TO SWIM THE WATERS OF THE EARTH.
Not only has the shape of the fish—or ichthyoid form, as it is called—served as a model for inventors of the submarine boat to go by, but the air-bladder in the fish, which aids it in keeping its place below the surface of the water, finds its counterpart in the ballast tanks of the modern submarine.
When the first real boy parted from his monkey cousin—that is, when the boy came down from his tree-top house and left the monkey up there to eat a banana all alone—Nature had fitted him with long legs and flat feet so that he might swiftly run away from his enemies on land.
But in those days when the earth was young there were not only gigantic, long-necked animals with cross-cut saw tails and cunning little heads, but terrifying winged lizards[5] flew around everywhere like airplanes do now, and monstrous and inconceivable things swam in the sea. He could easily outwit and outdistance his animal foes on land, but he could not fly away from those that sailed the air, nor could he venture far into the water for fear of his aquatic enemies. But he learned to swim in spite of them and when he could dive down here and come up over there he became the second submarine. (See [Fig. 2].)
FIG. 2. THE SECOND SUBMARINE. HE WAS THE FIRST HUMAN BEING TO PROPEL HIMSELF THROUGH THE WATER.
From the time he learned to swim and grew to be a man he nursed the idea of making some kind of device that he could get into and swim about with, not only so that he might be protected from the monsters that sought him as food but that he might destroy them as well.