It has been urged, and with apparent reason, that the value of espionage ceases as soon as armies take the field, since the work of the spy can only concern preparations for hostilities, and, when war has begun, actual strength decides the issue. This, however, is not the case when German military espionage is in question; in many cases the fixed agents have been so long established at their posts that they rank in the eyes of normal inhabitants as a part of the life of the place, and, by maintaining their positions, they are able to ascertain for the benefit of their own commanders particulars of the dispositions of hostile forces. Elaborate systems of signalling are in use; carrier pigeons are used, but only to a limited extent; the ways of the Red Indians, who made the most perfect spies ever known, are copied in indicating events by the movement of stones, chipping of bark on trees, breaking branches, and other ways little likely to be detected, while the more civilised method of lamp-signalling is also practised. Altogether, the German military spy forms a very efficient and formidable part of the German military force, both before and after the opening of hostilities. His value decreases to a certain extent when action has been entered on, and, in a definite battle like those along the line of the Meuse and the line of the Aisne, he is practically useless, but in case of an advance on the part of the German forces he is invaluable, by reason of the information he can give with regard to the nature of the country and the dispositions of the retreating army. CHAPTER FIVE. NAVAL ESPIONAGE.