We need hardly observe that we speak of the strategic flank, that is, a side of the theatre of war, and that the attack from one side in battle, or the tactical movement against a flank, must not be confounded with it; and even in cases in which the strategic operation against a flank, in its last stage, ends in the tactical operation, they can quite easily be kept separate, because the one never follows necessarily out of the other.
These flanking movements, and the flanking positions connected with them, belong also to the mere useless pageantry of theory, which is seldom met with in actual war. Not that the means itself is either ineffectual or illusory, but because both sides generally seek to guard themselves against its effects; and cases in which this is impossible are rare. Now in these uncommon cases this means has often also proved highly efficacious, and for this reason, as well as on account of the constant watching against it which is required in war, it is important that it should be clearly explained in theory. Although the strategic operation against a flank can naturally be imagined, not only on the part of the defensive, but also on that of the offensive, still it has much more affinity with the first, and therefore finds its place under the head of defensive means.
Before we enter into the subject, we must establish the simple principle, which must never be lost sight of afterwards in the consideration of the subject, that troops which are to act against the rear or flank of the enemy cannot be employed against his front, and that, therefore, whether it be in tactics or strategy, it is a completely false kind of notion to consider that coming on the rear of the enemy is at once an advantage