"I had, therefore, to be very careful not to rise too high and thus attract the attention of the torpedo-boats. Slowly the periscope rose above the surface, and I could see the enemy in front of me, and toward the left the east coast of England. I tried to turn to starboard, but the rudder did not work. In consequence, I had to sink again to the bottom of the sea, where I remained for six hours, at the end of which time I had succeeded in putting the compass in order, and also in repairing the steering-gear. But upon rising this time, we were detected by a torpedo-boat, which made straight for us, forcing me to descend again." (This apparently was before depth-bombs came into use.) "I remained submerged for two hours, then turned slowly outward, and at a distance of some fifty metres from the leading enemy craft, passed toward the open sea. At 9 o'clock in the evening we were able to rise and proceed in safety."
Here is a human document, is it not? It is the experience of the tarpon at the undersea end of the line, or, in human terms, the hidden drama of man against man, drama of the sort made possible by the ingenuity of this modern age.
Submarine-chasers are shallow craft, capable of a speed of thirty-five miles an hour or more, mounting guns fore and aft. Some of our chasers measure more than 200 feet over all (Eagle class), while others measure 110 feet. The British, as already said, like the 80-footer, although using all sizes. Well, in any event, the chaser cruises about looking for surface waves. Now, the surface wave is the path marked by a submarine on the surface of the water. Even when she is fifty feet below the surface she leaves this palpable pathway up above. And few submarines travel at a depth of sixty feet. Then besides this track there are air-bubbles and spots of oil, all confirming the presence beneath the water of the U-boat.
So thereafter the chaser simply follows that surface wave until the submarine comes to the surface, as she must do sooner or later to get her bearings and look about for prey. When she does come up—she goes down for good. The hunt of the chaser has been aided in the past year or so by the depth-bomb, which did not exist in the first two and a half years of war. Equipped with this, she need not necessarily follow a surface wave all day; she simply drops the bomb down through this wave; at least she does under certain conditions.
This depth-bomb, by the way, is a wonderful invention, and with its perfection began the great decrease in submarine losses. The bomb is cylindrical and has in the top a well in which is fitted a small propeller. As the water comes in contact with the propeller the sinking motion causes it to revolve. As it revolves it screws down a detonator which comes in contact with the charge at ten, fifteen, twenty, or forty or more feet as designated by the hand of an indicator on the bomb. The hand of this indicator is, of course, set by the officer before the bomb is released either from a gun or from tracks along the deck.
Then there have been a number of tricks; some of them Yankee tricks, some of them the creatures of the equally fruitful British tar. One day in the North Sea a British patrol-vessel came across a trawler. It resembled the ordinary British trawler, but there were points of difference, points that interested the inquisitive—and suspicious—commander of the war-vessel. Chiefly there were a lot of stores upon her deck. She flew the Norwegian flag, and her skipper said he was neutral. But the British commander decided to take a chance. He arrested the crew, placed them in irons, and manned the trawler with a crew of French and English navy men.