2.—Combination of Arms.
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.