Now, a submarine cannot see anything underwater. The commander cannot even see the bow of his boat from the conning-tower, and until he gets near enough to the surface to poke his periscope out of water he is absolutely blind and must feel his way about with compass and depth-gage. It was always an anxious moment for the U-boat commander, when he was coming up, until his periscope broke out of the water and he could get his bearings; and even that was attended with danger, for his periscope might be seen. Of course a periscope is a very insignificant object on the broad sea, but when a submarine is moving its periscope is followed by a wake which is very conspicuous, and so the U-boat ran a chance of being discovered and destroyed before it could dive again to a safe depth. Later, telescoping periscopes were used, which could be raised by means of a hand-lever. The submarine would run along just under the surface and every now and then it would suddenly raise its periscope for an observation and drop it down again under cover if there was danger nigh. This was much simpler and quicker than having a six-or eight-hundred-ton boat come up to the surface and dive to safety. He might even collide with a vessel floating on the surface, but to lessen this danger submarines were furnished with ears or big microphone diaphragms at each side of the hull by which a ship could be located by the noise of its propellers. In the bow were the torpedo-tubes and the magazine of torpedoes. At first there were only two torpedo-tubes, but later the number was increased to four. These were kept constantly loaded, so that the projectiles could be launched in rapid succession, if necessary, without a pause for the insertion of a fresh torpedo. In some submarines tubes were provided in the stern also so that the boat could discharge a torpedo at its enemy while running away from him. Each tube was closed at the outer end by a cap and at the inside end by a breech-block. The tube was blown clear of water by means of compressed air, and of course the outer cap was closed when the breech was open to let in a torpedo. Then the breech was closed, the cap opened, and the torpedo was discharged from the tube by a blast of air. THE TORPEDO A torpedo is really a motor-boat, a wonderfully constructed boat, fitted with an engine of its own that is driven by compressed air and which drives the torpedo through the water at about forty miles per hour. The motor-boat is shaped like a cigar and that used by the Germans was about fifteen feet long and fourteen inches in diameter. We used much larger torpedoes, some of them being twenty-two feet long. Ours have a large compressed-air reservoir and will travel for miles; but the Germans used their torpedoes at short ranges of a thousand yards and under, cutting down the air-reservoir as much as possible and loading the torpedo with an extra large explosive charge.