As we leaf through Mahan’s Treatise on Field Fortifications, the lesson plan offered, after defining components of the profile and trace, an important perspective for planning and evaluating fortifications – a connection between the attack and defense of the works:
The attack and defense of intrenchements bear a necessary relation to each other; and it is upon a knowledge of the course pursued by the assailant, that the principles regulating the defense should be founded.
Grant me some license for an analogy here and call this a symbiotic relationship. Symbiotic, that is, borrowed from biology and defining two organisms of different species that exhibit a long-term, close interaction. In the case of military affairs, the only reason a place would be defended with earthworks is because the defender feels an attacker might wish to gain possession. Furthermore, the defender would build the works specifically to counter (if not deter) the most likely form of attack. Likewise, the attacker would plan the assault based on knowledge of the layout of the defenses. In short, one plan will exist only because of the other, counter, plan. Otherwise, there’s simply no reason for the planned action – be that placing a defensive work or organizing an assault of the position.
Mahan elaborated further, providing the students a generalized example of what an attack looked like:
An attack is, generally, opened by a fire of the enemy’s artillery, whose objective is to silence the fire of the intenchments, and to drive the assailed from the parapet; when this object is attained, a storming party, which usually consists of a detachment of engineer troops, a column of attack, and a reserve, is sent forward, under the fire of the artillery, to the assault. The detachment of engineer troops proceeds the column of attack, and removes all obstacles that obstruct its passage into the ditch. The line of march is directed upon a salient, through a sector without fire, and on the prolongation of the capital, as this line is least exposed to the fire of the works.
Depicting that approach on Mahan’s figure:
See how this approach was designed to take advantage of an inherent flaw of the works? Mahan continued with more exploitation of the fortification flaws:
When the ditch is gained, the party makes its way to a re-entering angle, where, sheltered from the fire of the flanks, the work is entered by the column of attack, either by making a breach in the parapet, or else by means of ladders. The reserve supports the column of attack in case of need; and if it is driven from the works, covers its retreat.
Again, as that would look on Mahan’s figure:
This approach allowed the attacker to pick apart the defense by working under the parapet within the ditch inside the dead space, avoiding the angles of defense.
So how does that look from the defenders side?
The manner of making the defense is with artillery, musketry, the bayonet, and sorties. The enemy is attained at a distance by the fire of the artillery and musketry, whose effect will chiefly depend upon the length of time that he is kept exposed to it by the ditch, and the obstacles in front of it. The bayonet is resorted to, as soon as the enemy shows himself on the berm; and sorties are made, either when any irresolution or confusion is seen in the enemy’s ranks, or at the moment he is repulsed from the parapet.
Note that Mahan didn’t emphasize here the nature of the parapets, faces, and flanks in order to build the perfect defensive line. That technical perspective he saved for a more detailed explanation. Instead he focused on what the defender could do with their weapons. Implied in the notion of the sortie is that the defender retained high motivation to conduct such a counter-attack. And with that, Mahan is admitting that flaws would be present in any defense. To mitigate those flaws, where existing, the defender applied cold steel, hot lead, flesh, and bone.
But you see here how the nature of attack and defense fit against each other. The attack had to be planned with a mind to exploit the flaws of the defense. The defense had to be planned to minimize those flaws. After establishing that symbiotic relationship, Mahan proceeded to lay out nine principles of the defense – some technical, others tactical, and yet others addressing the “spirit” of the defenders. We’ll take a look at those next week.
(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, pages 5-6.)