He adds that he knew all about that cruiser, and she knew all about him. Otherwise he would not have shown even his periscope; and if he had, she would have had a shell into him by now, and a depth-charge to follow. A depth-charge is perhaps the most formidable weapon against which the submarine has to be on guard. It is a bomb, with a detonator which can be set to explode when it reaches any given depth. A small one would need to hit the mark full, or be very close to it, in order to get a satisfactory result; but the newer and larger ones will seriously damage a submarine within an area of forty yards. The charge is either dropped over the stern of the pursuing vessel, when she is thought to be just over or just ahead of the enemy; or it is fired out of a small and handy short-range howitzer--a kind of lob-shot, a number of which can be made by several patrol boats acting together, so as to cover a larger area with much less risk of embarrassing each other. Even if the submarine is not destroyed outright, the chances are in such a case that she will be so damaged as to be forced to the surface or to the bottom, and then the end is certain. A bad leak would bring her up--an injury to her tanks or rudders might drive her down. You are uncomfortably reminded once more of that inherited dislike of death by suffocation. If a submarine cannot rise to the surface, you ask, is there no possible means of escape? The answer is that it may be possible, with great difficulty, to get out of the boat; but there is very little chance that you would survive. The lungs are not fitted to bear so great and sudden a change of pressure as that felt in passing from the boat to the water, and from the deep water to the surface. You are perhaps surprised; but the pressure of sea-water at 160 feet is equal to five atmospheres, or about 75 lbs. to the square inch. To pass safely through this to the ordinary surface atmosphere would need a long and gradual process, and not a sudden rise of a few seconds. A very brave attempt was made on one occasion, when a British submarine had gone to the bottom during her trials, and could not be got up by any effort of her crew. The agony of the situation was intensified by the fact that help was close at hand, if only the alarm could be given, and the whereabouts of the submarine communicated to the rescuers. The officers of the sunken boat were, of course, perfectly aware of the danger from sudden change of pressure; but one of them volunteered to go to the surface, alive or dead, and carry a message on the chance of attracting some ship’s attention. To lessen the risk as far as possible, it was arranged that he should go up into the conning-tower, and that the hatch should then be closed beneath him and the water gradually admitted. As it flowed slowly in, and mounted round him, the air in the top of the conning-tower would diminish in extent but increase in pressure. When it reached his neck, the internal pressure