(Book Five) Chapter Four: Relationship between the Branches of the Service
Here we shall only discuss the three main branches: infantry, cavalry, and artillery.
We trust we may be forgiven the following analysis, which really belongs more under the heading of tactics. It is needed here in the interest of clarity.
An engagement consists of two essentially different components: the destructive power of firearms, and hand-to-hand, or individual, combat. The latter in turn can be used for either attack or defense (words employed here in an absolute sense, for we are speaking in the broadest terms). Artillery is effective only through the destructive power of fire; cavalry only by way of individual combat; infantry by both these means.
In hand-to-hand fighting, the essence of defense is to stand fast, as it were, rooted to the ground; whereas movement is the essence of attack. Cavalry is totally incapable of the former, but preeminent in the latter, so it is suited only to attack. Infantry is best at standing fast, but does not lack some capacity to move.
This distribution of elementary military strengths among the three main arms demonstrates the superiority and versatility of infantry in comparison with the other two: it alone combines all three qualities. This also explains how in war a combination of the three arms leads to a more complete use of all of them. It enables the combatant to reinforce at will any one of the functions which, in the infantry, are inseparably united.
In recent wars the major role has undoubtedly been played by the destructive power of firearms: but it is no less clear that the true, the actual core of an engagement lies in the personal combat of man against man. An army composed simply of artillery, therefore, would be absurd in war. An army consisting simply of cavalry is conceivable, but would have little strength in depth. An army consisting simply of infantry is not only conceivable, but would be a great deal stronger. The degree of independence of the three branches, then, is infantry, cavalry, artillery.