A valve is opened, and air is allowed to escape from the water-ballast tanks in the bottom of the vessel. Water flows in, and the submarine sinks until she is running "awash," with the base of the conning-tower only just clear of the waves. She is now ready to dive. This she must do before getting within range of the cruisers out yonder. There are hundreds of keen eyes on the British warships, and even the conning-tower of a submarine a mile away will be seen. A wheel is moved, the boat tilts downward slightly at the bows, and in a few moments the water is swirling round the windows of the conning-tower. Diving has begun. Down, down she goes. Presently the wheel is moved again, and the boat returns to an even keel. The only part of her that now shows above the water is the periscope. The commander glues his eyes to the mirror which gives him a view of the sea around. The images of the cruisers grow larger and larger; one of them, H.M.S. _Birmingham_, is now within range. He moves his boat so that the torpedo tube at her bow points directly towards the _Birmingham_. His hand hovers over the switch which will launch a torpedo on its death-dealing errand. Why risk missing to avoid the slight danger of discovery? Another five hundred yards, and then---- The fateful moment has come. His hand slightly trembles with excitement as he prepares to make the trifling movement which may send some hundreds of men to a watery grave, and a gallant ship, worth more than a million of money, to the bottom. [Illustration: This picture gives an excellent view of a torpedo and its tube on board a destroyer. The tube, you will observe, can be trained like a gun, and thus a correct aim can be taken.] [Illustration: This diagram gives a section of a torpedo, which has been well described as a complete little warship. It has engines to drive it along; rudders to steer it; a special apparatus to make it return to the line of fire, if it should swerve; a supply of explosives to damage the enemy, and apparatus for firing the explosive at the right moment. A torpedo such as is used in our navy costs £1,000. Warships at anchor have steel nets around them as a protection against torpedoes. Some torpedoes, however, are fitted with a pair of powerful wire cutters, which enable them to pierce the net and strike the ship.] He presses the button; a flap opens in the tube in the bows; a valve admits compressed air into the rear end of it, and a shining torpedo leaps forward towards the quarry.