To the difficulty provided by the desire for concealment necessary in all military organization, one must add the difficulty presented by the cross categories peculiar to this calculation. You have to consider not only the distinction between active and reserve, but also between men and munitions, between munitions available according to one theory of war, and munitions available according to another. You have to modify statical conclusions by dynamic considerations (thus you have to modify the original numbers by the rate of wastage, and the whole calculus varies progressively with the lapse of time as the war proceeds). In spite of these difficulties, I believe it to be possible to put before the general reader a clear and simple table of the numbers a knowledge of which any judgment of the war involves, and to be fairly certain that this table will, when full details are available, be discovered not too inaccurate. We must begin by distinguishing between the two sets of numbers with which we have to deal--the numbers of men, and the amount of munitions which these men have to use. The third essential element, equipment, we need not separately consider, because, when one says "men" in talking of military affairs, one only means equipped, trained, and organized men, for no others can be usefully present in the field. Let us start, then, with some estimate of the number of men who are about to take part in battle; let us take for our limits the convenient limits of a year, and let us divide that space of time arbitrarily into three parts or periods. There was a first period in which the nations opposed brought into the field the men available in the first few weeks for immediate action. It is not possible to set a precise limit, and to say, "This period covers the first six" or "the first eight weeks;" but we can say roughly that, when we are speaking of this first period, we mean the time during which men for whom the equipment was all ready, whose progress and munitioning had all been organized, were being as rapidly as possible brought into play. Such an estimate is not equivalent to an estimate of the very first numbers that met in the shock of battle; those numbers were far smaller, and differed according to the rate of mobilization and the intention of the various parties. The estimate is only that of the total number which the various parties could, and therefore did, bring into play before men not hitherto trained as soldiers, or trained but not believed to be required in the course of the campaign--according as that campaign had been variously foreseen by various governments--came in to swell the figures.