The Boy Volunteers with the Submarine Fleet Part 6

"Two," was the laconic reply.

"How long have we been submerged?"

"Two hours," answered the man. "As I came down the report from the periscope showed a clear sea, and we are now about to resume surface travel and repair one of the periscopes."

The boys glanced at each other and at the captain.

"Yes," remarked the captain, "that was a pretty close call."

The attendant left them without closing the door, and as the prisoners glanced about, nothing was to be seen of the stairway which led to the conning tower. Men were noticed at work, each being stationed at some particular machine or set of machinery. Then, with a bang, something like a trap door swung aside and the stairway was revealed, and a peculiar light streamed in through the hatch opening.

"It's the sun," said Ralph, in ecstacy.

"I never thought we'd see that again," said Alfred, almost overcome.

"May we walk around?" asked the captain, as he approached an under officer.

"There isn't much chance for exercising here," was the reply, "but I think you will be given top liberty after awhile," replied the man.

"Will they let us go?" asked Ralph eagerly.

"No; he didn't say that; he meant they would give us liberty to walk on the top deck for a short time," replied the captain.

Shortly thereafter the lieutenant in command of the submarine appeared at the foot of the hatchway and informed the captain that they were at liberty to ascend. Never did the sun appear to be more beautiful or inviting, although there was a perceptible chill in the atmosphere. The submarine was moving along at a speed of twelve knots an hour. Four men were engaged in taking down a bent and partially ruptured periscope tube.

The captain glanced at it and drew the attention of the boys to its structure. It was the tall periscope that received the shot, which struck it about four feet from the top.

"It must have been hit on the water line," said the captain, addressing the lieutenant.

The latter merely nodded, but made no remarks in response.

They were permitted to walk to and fro for an hour, when the order came to descend, and they again entered their prison. As before, they were subjected to total darkness, but there was no necessity for this deprivation, and it is not clear why an enemy should treat prisoners in this manner, for such actions necessarily leave only resentments and do no good whatever.

It was a long, long, dreary afternoon and night, which they tried to while away in sleeping, for conversation, under the circ.u.mstances, soon became irksome. When they awoke, or, rather, when all were again alert and felt as though the night must have pa.s.sed, the captain was the first to break the silence, as he said:

"We have been resting quietly for more than an hour, I should say, probably lying in wait in one of the steamer lanes for new victims."

"Isn't it likely we are on the bottom of the ocean? Don't they go down sometimes and wait there?" asked Ralph.

"Yes; but not in deep water, such as is found in this bay. At no place is it less than 150 fathoms, and in the central portion, where our s.h.i.+p went down it is more than 2,000 fathoms."

"Why, that's two miles deep, or more," said Alfred.

"Yes, the Bay of Biscay is one of the deep holes in the Atlantic coast line of Europe. The average depth of the Irish Sea, St. George Channel, the English Channel and the North Sea is only about 250 feet, and there are thousands of places in the North Sea, particularly, like the Dogger Banks, where the water is not more than a hundred feet deep," remarked the captain.

"Then the submarines could easily rest on the bottom if the depth is not more than one hundred feet?" asked Alfred.

"Submarines have, in several cases, gone down as far as 200 feet below the surface, but it is at a great risk," said the captain.

"You mean risk from the pressure of the water?" said Ralph.

"Yes," was the reply.

"What would be the pressure of the water on a submarine at that depth?"

asked Alfred.

"Pressure is calculated on the square inch of surface; for every twenty-eight inches the pressure is equal to one pound. If, therefore, 200 is multiplied by 12 and then divided by 28, the quotient will represent the number of pounds on each square inch," answered the captain.

"Why multiply 200 by twelve?" asked Ralph.

"Because there are twelve inches in a foot," said the captain.

"Oh, yes; I didn't happen to think of it; well, 200 by 12,--that's 2,400, and divided by 28, is----"

"Eighty-five," interrupted Alfred. "Well, that's not very much."

"Quite true," rejoined the captain; "but how many square inches are there in a square foot?"

"One hundred and forty-four," replied Alfred.

"Then, eighty-five times one hundred and forty-four makes quite a sum,"

continued the captain.

"Whew,----" said Ralph with a half whistle in his tone, "why, if I have made it out right, it's over 12,000 pounds. No wonder it isn't safe to stay down very long, if at all, at that depth."

"I have often wondered how it is that the submarine could rest on the bottom or come up at will," said Alfred.

"All submarines are lighter than the water in which they float,"

answered the captain. "They are provided with tanks holding compressed air. Now, in order to submerge, the only thing necessary is to permit enough water to flow into special tanks within the submarine, until the combined weight of the water, hull and mechanism, is the same as the amount of water that the s.h.i.+p displaces. If an added quant.i.ty of water is now added, it will go down, and remain under water until the air in the compressed tanks is used to force out a quant.i.ty of water from the special tanks."

"But is that the only way they can go down?" asked Ralph.

"Oh, no; a submarine can submerge without doing that, but in such a case power must be used," answered the captain.

"What! push it down by power?" asked Alfred.

"Exactly; these vessels have fins, the same as fish, so arranged that if they are properly turned and the s.h.i.+p moves forward, it will dive, and continue to go down at an angle as long as the fins are properly set. If the vessel should stop moving the submarine would come to the top, because it is lighter than the water," responded the captain.

CHAPTER V

SOME OF THE MYSTERIES OF A SUBMARINE

With a click the door of their prison cabin opened and a seaman informed them that their breakfast was ready. They pa.s.sed through the narrow door, and edged their way along a tortuous path that led to the rear, where they entered what might be called a miniature galley, on one side of which was a narrow shelf containing food of various descriptions.