trustworthy, and at the same time has to be synthesized in an
atmosphere of hurry and high tension, and interpreted, often
without waiting for checks and confirmations, for a commander-
in-chief who may well hesitate to stake everything on its accuracy.
Nevertheless, during the World War the service of military
intelligence reached a level of accuracy and usefulness that it
had never reached in any previous war. This success was due
(a) to the rapidity of modern means of communication, (ft) to
the enormous volume of the data obtained, and (c) to the rapid
development of aviation. These causes taken together both
compelled and justified an elaborate organization of the intelli-
gence service both in War Offices and in field armies.
In considering the organization it is better to ignore the dis- tinction between War Office and G.H.Q., and to differentiate, instead, between the central intelligence system of which cer- tain branches and representatives live and work at G.H.Q., others in Allied and neutral countries and the rest at the War Office and the field intelligence system. The central intelli- gence system in all cases carries out all the processes collec- tion, synthesis, interpretation in connexion with the enemy's forces, recruiting and losses, internal condition and moral, eco r nomic condition, armament and equipment. When there are several important theatres of war, it is also the final focus of information, and interpreting authority, for the enemy's order of battle, and organization, distribution of force to the different theatres, inter-theatre movements, general plan of campaign, military moral, quality of troops, characteristics of leaders and tactical methods. It is, further, the authority responsible for passing information derived from one theatre to other theatres so far as it concerns them. To it belong all organs of the secret service and the counter-intelligence service together known in Great Britain as I(b) whether working in a theatre of war or not. It is an open question whether counter-intelligence (which lives mentally on its own side of the line) and positive intelligence (which lives on the enemy's) should logically form part of the same organization, but it is clear in any case that all branches of intelligence which employ secret means of news- gathering should belong to one system, which is the central.
To field intelligence, on the other hand, belong essentially the study, within the theatre of war, of enemy plans, as revealed by his distribution of force, movements, and front and rear works. If the theatre of war is single, some functions normally " central " such as moral, order of battle, tactical methods may come within its scope. Indeed there may be campaigns in which field intelligence absorbs central intelligence com- pletely. In the past, with imperfect means of liaison between home and headquarters, this was often the case even in European campaigns, while as regards warfare in undeveloped countries it is often so still. But in war on the scale of the World War, in which the front and the rear, the soldier and the citizen, the gunner and the scientist, react upon one another incessantly, it was imperative to organize the intelligence service effectively, if not formally on the basis of a central system for the whole and a field system for each theatre. This logical distinction does not mean that central intelligence and field intelligence operate in watertight compartments. Each is indispensable to the other in a dozen ways. For instance, at the very least half of the data used by central intelligence in determining the enemy's battle order are obtained by field intelligence, and central intelli- gence, through interrogations of rapatries and refugees, con- tributes essential details to the stock of field intelligence.
The Central Intelligence System. We may now consider the several elements which make up the work of central intelligence.
The enemy's order of battle is the most important of all classes of intelligence. It forms the foundation upon which is based the greater part of intelligence, reasoning and calculation. Once it is established, variations both of organization and of plan can be followed almost day by day. Forming as it does the framework upon which the enemy's units are built up into armies, it is so rigidly respected in practice that from the cap- ture of three soldiers it may be not only possible but safe to deduce the pressure of a division at A. and incidentally its with-
drawal from its previous position at B., even though these soldiers remain silent under questioning. To the layreader it may seem a simple and obvious course for the enemy command to delude intelligence by constant changes in the order of battle. So it is. But such changes seriously impair efficiency, and as a rule " the game is not worth the candle." This was preemin- ently true of the German army in the World War. Except at certain crises, in which the only possible course was to seize a battalion here and a brigade there and fling it into the fight, the German order of battle was built up in perfectly logical sequence from the original 25 army corps of peace-time, and, once built up, was maintained till the summer of 1918.
The strength, recruiting and losses of the enemy are studied minutely by organs of the central intelligence both in the field and at home. The sources are, amongst others, statistical enquiries in the prisoners' camps or cages, captured documents, agents' reports from the interior of the enemy's country and the demographic and industrial statistics collected both in peace and in war. Strength is measured partly by multiplying aver- age unit and divisional strengths found in establishing and main- taining the enemy's "order of battle," partly by watching the calling-up of recruit classes in the enemy's home territory. Field strength in relation to available man-power is estimated by careful work on economic data, on the munitions legislation of the enemy's country, by reading letters from home found on prisoners and generally by synthesizing and interpreting very miscellaneous data. An estimate of losses of course forms an essential ingredient of strength estimates and this is formed by studying published casualty lists, working on captured returns, and " analysing " prisoners. This statistical examination of prisoners (if these are available in large numbers) is very valu- able, as it shows the composition of typical units of the enemy, his system of replacing casualties, and his man-power.
In the study of the enemy's general plan of campaign, his allocation of force to different theatres and his inter-theatre movements, the data are obtained both by organs of the central intelligence and by the intelligence systems in the field; they undergo, as they pass to the central system, a process of gradual synthesis and crystallization. Other data of a collateral kind come from the political and economic intelligence systems, which are, or should be, asked to contribute not mere data (i.e. items), but considered interpretations of the political or economic situation. In these, the highest levels of intelligence work, only the head of the service and a few of his closest and most responsible assistants are concerned; its importance can scarcely be exaggerated, and the synthesis must be so sound that the interpretation can bear the anxious cross-examination of the command and the Cabinet.
Intelligence work on enemy armament and equipment differ somewhat from other branches in that it deals with concrete objects rather than with estimates and appreciations, and moreover requires the services of technicians, either as per- manent members of intelligence or as consultants. In its nature this work belongs to the central system. Enemy material is of interest as indicating (a) the scale and principles upon which the opponent is armed, (b) new weapons or apparatus, and modifications of old ones, which may be worth copying and in any case have to be reckoned with, (c) the state of the enemy's munition industries with regard to raw materials, with as its corollary the appearance of new industrial processes. In each of these cases as indeed in all intelligence work the essence of success is continuous collection of and systematic reporting on varied items. Thus, a new shell used by the enemy may be reconstructed from fragments even before an unexploded speci- men is obtained. A new pattern of gun though it uses a fa- miliar shell may betray itself by the number and inclination of grooves engraved in the driving band, by a " shelling con- nexion " established between the battery position and the point of impact and by other methods. Fuzes even percussion fuzes have a story to tell to the expert, and cast-iron pro- jectiles, chlorate explosives, paper machine-gun belts, steel car- tridge cases, interest the economist who is studying the enemy's
