Spy, in War, is a useful but not highly honoured auxiliary employed to collect information and ascertain the enemy's intended operations. Spies are always used in war, and their employment is quite recognised by the law of nations as interpreted by Grotius, Vattel, and Martens; nor is it held to be any dishonour to a general to avail himself of their services. On the other hand, the spy himself is looked upon as an outlaw, and when taken is put to death ignominiously and without mercy. A spy is well paid, lest he betray his employer. In the British army spies are employed by the Intelligence branch under the quartermaster-general. In minor expeditions they are generally friendly natives. Military law, though distinct enough in ordering his death, is not clear in defining what constitutes a spy. A man, not belonging to the army, found within the lines, either in uniform or civil dress, if unable to give a good account of himself would certainly be arrested as a spy, and if anything suspicious could be proved against him would probably be hanged or shot; but if found in one camp in the uniform of the opposite side, he may not be treated otherwise than as a prisoner of war, or else as a deserter from the enemy.
Both as regards honour and penalties, it would seem that spies ought in fairness to be divided into two classes—first, those who betray their own country to an enemy (either in time of war or peace, and including persons who give foreign powers plans of fortifications, betray the construction of new weapons, &c.); secondly, those who, being enemies, contrive surreptitiously to obtain information by penetrating into the lines of the opposing army. The first class are traitors of a deep dye, for whom no ignominious death is too bad; but the second class are brave men, who dare much in the service of their country. It is unfair to accord them the same treatment as the traitors. André (q.v.) was a spy; Benedict Arnold (q.v.) was a traitor.
Civil governments, even the freest and most constitutional, do not disdain to make use, on occasion, of political spies—the most respectable use for them being the ferreting out of conspiracies and conspirators. In the days of the Tudors the political spy was a frequent and almost recognised ally of great English ministers like Burghley; in Ireland, unhappily, government has not seldom had to employ the services of Approvers (q.v.), Informers (q.v.), and also of professional spies (see Fitzpatrick, Secret Service under Pitt, 1892). The Secret Service Moneys (q.v.) provide for the remuneration of such persons as Le Caron of the 'Parnellism and Crime' trial in 1889, who had entered the Fenian organisation, the United Brotherhood or Clan-na-Gael, &c., and kept the government informed of all that went on in these societies. Bismarck was believed to regularly employ sham revolutionists; the second French empire had an elaborately organised system of espionage. Austria had at one time the most active agents of any European country, especially in the parts of Italy under Austrian domination. And at the present day the Russian system is the most masterful, being almost untrammelled at home, and, in the less ignoble parts of the service, represented abroad by ladies and gentlemen of great culture and high social standing. The political spy, acting in his own country, is hard to distinguish from the detective; it will often be difficult to draw a line between the spy abroad and the renegade or traitor on the one hand, and the political agent. See Caron, Twenty-five Years in the Secret Service (1892).