Further, the naval spy is made acquainted with the build and outline of every class of naval vessel in the world. He is first schooled in the details of the various battleships, cruisers, and smaller craft belonging to the Great Powers, and, later, is taught to recognise these vessels by silhouettes, from which he gains sufficient knowledge to recognise any ship either by day or night--assuming that the night is of such a character that the ship is at all visible. He studies uniforms and insignia of rank, signals and codes, and at the end of his training is a fully qualified naval officer so far as the theory of naval matters goes. In the yards of Wilhelmshaven and Kiel is opportunity of putting his knowledge to the test, and he has to satisfy his examiners on all the points on which he has been coached. With regard to diplomatic espionage, the coaching bestowed on the two branches already mentioned is not undertaken, for the diplomatic spy--in the narrower sense of the phrase, since all spies must be extremely diplomatic--is chosen, as a rule, from among the ranks of naval and military spies. In order to undertake diplomatic missions, and supplement the work of the German embassies in the various European centres, a spy must be a very good man indeed, as far as his work is concerned. He must be as was Stieber, absolutely ruthless and without scruple; he must be a good linguist, a man of good presence and address, and a tactful man as well. The corps of diplomatic spies is a small one, for this work is the best paid of all, the most delicate and intimate of all, and it is not a class of work of which there could ever be enough for a large staff, even in the state of European politics that existed at the outbreak of this last German war, since the diplomats of Germany are themselves sufficient, as a rule, for all needs of this kind. The diplomatic spy is called in for services which a diplomat is unable to undertake, and also as a check on the work of diplomats--he is, as it were, a member of a system which assures the efficiency of the diplomatic system. His training lies in the commissions entrusted to him in military and naval capacities: by super-excellence in the performance of his duties in these departments, he shows himself sufficiently able and efficient to warrant his being trusted with less obvious and more confidential tasks. He works, as do all the members of the German spy system, independently of all other workers for the good of the State. For in every case the spy works alone, lest in compassing his own downfall he should bring about that of others as well. This was a principle inaugurated by Stieber, who believed in trusting no man more than was absolutely unavoidable.