WE have only allotted to this prominent conception, in the world of ordinary military theory, a special chapter in dictionary fashion, that it may the more easily be found; for we do not believe that anything independent in itself is denoted by the term.
Every position which is to be held, even if the enemy passes by it, is a flank position; for from the moment that he does so it can have no other efficacy but that which it exercises on the enemy's strategic flank. Therefore, necessarily, all strong positions are flank positions as well; for as they cannot be attacked, the enemy accordingly is driven to pass them by, therefore they can only have a value by their influence on his strategic flank. The direction of the proper front of a strong position is quite immaterial, whether it runs parallel with the enemy's strategic flank, as Colberg, or at right angles as Bunzelwitz and Drissa, for a strong position must front every way.
But it may also be desirable still to maintain a position which is not unassailable, even if the enemy passes by it, should its situation, for instance, give us such a preponderating advantage in the comparative relations of the lines of retreat and communication, that we can not only make an efficacious attack on the strategic flank of the advancing enemy, but also that the enemy alarmed for his own retreat is unable to seize ours entirely; for if that last is not the case, then because our position is not a strong, that is not an unassailable one, we should run the risk of being obliged to fight without having the command of any retreat.
The year 1806 affords an example which throws a light on this. The disposition of the Prussian army, on the right bank of the Saal, might in respect to Buonaparte's advance by Hof, have become in every sense a flank position, if the army had been drawn up with its front parallel to the Saal, and there, in that position, waited the progress of events.
If there had not been here such a disproportion of moral and physical powers, if there had only been a Daun at the head of the French army, then the Prussian position might have shown its efficacy by a most brilliant result. To pass it by was quite impossible; that was acknowledged by Buonaparte, by his resolution to attack it; in severing from it the line of retreat even Buonaparte himself did not completely succeed, and if the disproportion in physical and moral relations had not been quite so great, that would have been just as little practicable as the passing it by, for the Prussian army was in much less danger from its left wing being overpowered than the French army would have been by the defeat of their left wing. Even with the disproportion of physical and moral power as it existed, a resolute and sagacious exercise of the command would still have given great hopes of a victory. There was nothing to prevent the Duke of Brunswick from making arrangements on the 13th, so that on the morning of the 14th, at day-break, he might have opposed 80,000 men to the 60,000 with which Buonaparte passed the Saal, near Jena and Dornburg. Had even this superiority in numbers, and the steep valley of the Saal behind the French not been sufficient to procure a decisive victory, still it was a fortunate concurrence of circumstances, and if with such advantages no successful decision could be gained, no decision was to be expected in that district of country; and we should, therefore, have retreated further, in order to gain reinforcements and weaken the enemy.
The Prussian position on the Saal, therefore, although assailable, might have been regarded as a flank position in respect to the great road through Hof; but like every position which can be attacked, that property is not to be attributed to it absolutely, because it would only have become so if the enemy had not attempted to attack it.
Still less would it bespeak a clear idea if those positions which cannot be maintained after the enemy has passed by them, and from which, in consequence of that, the defensive seeks to attack the assailant's flank, were called flank positions merely because his attack is directed against a flank; for this flank attack has hardly anything to do with the position itself, or, at least, is not mainly produced by its properties, as is the case in the action against a strategic flank.
It appears from this that there is nothing new to establish with regard to the properties of a flank position. A few words only on the character of the measure may properly be introduced here; we set aside, however, completely strong positions in the true sense, as we have said enough about them already.
A flank position which is not assailable is an extremely efficacious instrument, but certainly just on that account a dangerous one. If the assailant is checked by it, then we have obtained a great effect by a small expenditure of force; it is the pressure of the finger on the long lever of a sharp bit. But if the effect is too insignificant, if the assailant is not stopped, then the defensive has more or less imperilled his retreat, and must seek to escape either in haste and by a detour—consequently under very unfavourable circumstances, or he is in danger of being compelled to fight without any line of retreat being open to him. Against a bold adversary, having the moral superiority, and seeking a decisive solution, this means is therefore extremely hazardous and entirely out of place, as shown by the example of 1806 above quoted. On the other hand, when used against a cautious opponent in a war of mere observation, it may be reckoned one of the best means which the defensive can adopt. The Duke Ferdinand's defence of the Weser by his position on the left bank, and the well-known positions of Schmotseifen and Landshut are examples of this; only the latter, it is true, by the catastrophe which befell Fouque's corps in 1760, also shows the danger of a false application.