Further, the military spy must know units of the British Army at sight, and must have at hand if not actually in his mind the code-word by which each unit is tabulated at Berlin. He must know the code-words, also, for various patterns of gun, must be conversant with classes of explosive and patterns of shell, and must be able, if luck and his own ingenuity should favour him, to carry in his mind sufficient of the nature and plan of a fortification to be able to draw a map of the work to scale, as nearly as possible, from memory. In all purely technical details of his work the military spy is trained in matters military before he sets out on the smallest piece of work, and he passes examinations just as a member of the military service would, except that his examinations are stiffer than those of the officer, and he is required to know all where the officer is only asked to acquire a part. For, in technical matters, the military spy must never be at a loss; he must be able to place guns and men, works and engineering details, with accuracy, since misinformation is worse than none. In the actual method employed in obtaining information much is left to the judgment of the spy. It is a platitude that no two battles are ever identical in character, and thus the plans of military commanders must vary with the line of country, the strength of the forces engaged, and many other points: in the same way the spies who pave the way for Germany's soldiers are never confronted by the same conditions twice, and they must adapt their methods to fit the circumstances of each case. In this, the more delicate and difficult part of their work, no amount of training can avail them, but all depends on their natural ability to make use of men and circumstances, a quality which is more to be classed as work than as training, since it is either part of the composition of a man, or is definitely lacking and not to be imparted by any training. Naval spying is practically analogous with military work in character, except that all the training must be devoted to familiarity with the details of naval work and construction--in the matter of coast fortifications, the work of naval and military spies overlaps to a certain extent. But, in addition to coast defence works and dockyards, which call for the activities of both naval and military spies, there are the details of every class of battleship to be learned. Topography is the first point, common to both branches, and trigonometry is an accessory to this, practically. But naval construction and drawing are peculiar to the naval spy, who is handed on to the care of an expert officer of the German Naval Intelligence Department, as a rule, and so familiarised with the details of various classes of torpedoes, mines, submarines, and guns, that he is able to recognise any one of these things at a glance, and tell the particular class and power which it represents.