"shadow" German submarines; it got each submarine "up in the morning and put it to bed at night." That is to say, the intelligence department took charge of Fritz and his crew as they emerged from their base, and kept an unwearied eye upon them until they sailed back home. The great chart in the convoy room of the Admiralty showed, within the reasonable limits of human fallibility, where each submarine was operating at a particular moment, and it also kept minute track of its performances.
Yet it was not so difficult to gather this information as may at first be supposed. I have already said that there were comparatively few submarines, perhaps not more than an average of eight or nine, which were operating at the same time in the waters south and west of Ireland, the region with which we Americans were most concerned. These boats betrayed their locations in a multitude of ways. Their commanders were particularly careless in the use of wireless. The Germanic passion for conversation could not be suppressed even on the U-boats, even though this national habit might lead to the most serious consequences. Possibly also the solitary submarine felt lonely; at any rate, as soon as it reached the Channel or the North Sea, it started an almost uninterrupted flow of talk. The U-boats communicated principally with each other, and also with the Admiralty at home; and, in doing this, they gave away their positions to the assiduously listening Allies. The radio-direction finder, an apparatus by which we can instantaneously locate the position from which a wireless message is sent, was the mechanism which furnished us much of this information. Of course, the Germans knew that their messages revealed their locations, for they had direction finders as well as we, but the fear of discovery did not act as a curb upon a naturally loquacious nature. And we had other ways of following their movements. The submarine spends much the larger part of its time on the surface. Sailing thus conspicuously, it was constantly being sighted by merchant or military ships, which had explicit instructions to report immediately the elusive vessel, and to give its exact location. Again it is obvious that a submarine could not fire at a merchantman or torpedo one, or even attempt to torpedo one, without revealing its presence. The wireless operators of all merchant vessels were supplied
