For strategy the combination of the three arms in the order of battle is only important in regard to those parts of the army which, according to the usual order of things, are likely to be frequently employed in a detached position, where they may be obliged to engage in an independent combat. Now it is in the nature of things, that the members of the first class, and for the most part only these, are destined for detached positions, because, as we shall see elsewhere, detached positions are most generally adopted upon the supposition and the necessity of a body independent in itself. In a strict sense strategy would therefore only require a permanent combination of arms in army corps, or where these do not exist, in divisions, leaving it to circumstances to determine when a provisional combination of the three arms shall be made in subdivisions of an inferior order. But it is easy to see that, when corps are of considerable size, such as 30,000 or 40,000 men, they can seldom find themselves in a situation to take up a completely connected position in mass. With corps of such strength, a combination of the arms in the divisions is therefore necessary. No one who has had any experience in war, will treat lightly the delay which occurs when pressing messages have to be sent to some other perhaps distant point before cavalry can be brought to the support of infantry—to say nothing of the confusion which takes place. The details of the combination of the three arms, how far it should extend, how low down it should be carried, what proportions should be observed, the strength of the reserves of each to be set apart—these are all purely tactical considerations. 3.—The Disposition. The determination as to the relations in space, according to which the parts of an army amongst themselves are to be drawn up in order of battle, is likewise completely a tactical subject, referring solely to the battle. No doubt there is also a strategic disposition of the parts; but it depends almost entirely on determinations and requirements of the moment, and what there is in it of the rational, does not come within the meaning of the term “order of battle.” We shall therefore treat of it in the following chapter under the head of _Disposition of an Army_. The order of battle of an army is therefore the organisation and disposition of it in mass ready prepared for battle. Its parts are united in such a manner that both the tactical and strategical requirements of the moment can be easily satisfied by the employment of single parts drawn from the general mass. When such momentary exigency has passed over, these parts resume their original place, and thus the order of battle becomes the first step to, and principal foundation of, that wholesome methodicism which, like the beat of a pendulum, regulates the work in war, and of which we have already spoken in the fourth chapter of the Second Book. CHAPTER VI. General Disposition of an Army