Fortification Friday: Complex “Intrenchments” and complexity fortification history

Earlier in this series, we looked at a class of fortification that Mahan labeled “simple fortifications.”  These included some well recognized – and some often misidentified – fortification layouts… “the Right Line; the Redan; the Lunette, or Detached Bastion; the Crémaillère, or Indented Line; the Priest-Cap, or Swallow-Tail; the Redoubt; the Star Fort; and Bastion Fort.”  And these were, for emphasis, “simple” in relative terms in regard to the level of effort required for the engineer to design the works.  Briefly, the simple entrenchments (or, if you prefer, fortifications) allowed the engineer to focus simply on a single point to be defended or single intended purpose… simply… for sake of redundancy.

But if there are simple entrenchments, there must be complex ones also, right?  Indeed.  And how do we define those complex entrenchments… or as they were called in Mahan’s day “intrenchments?  Well… as with many other things, Mahan avoided a specific definition.  Almost as if he wanted the cadets to focus more on the practical application than the theory.  But we can derive a general definition of “complex” from the description of the forms constituting these arrangements:

Lines or Complex Intrenchments.

Dispositions made to cover extended positions, and which present a front in one direction to the enemy, are termed Lines.  There are two classes of lines – Continued Lines, and Lines with Intervals.  Continued lines present no openings through which the enemy can penetrate except the ordinary outlets.  Lines with intervals consist of detached works, which are enclosed partly, or entirely, throughout their perimeters, arranged in defensive relations with each other; and presenting wide intervals between them defended only by their fire.

Implied here are three notions.  First, that complex entrenchments are actually a super-set of simple works arranged to present a front.  Second, that complex entrenchments are, as an aggregate, not just defending a salient point of importance, but rather the whole of an area.  Lastly, complex entrenchments, as the title “lines” implies, are erected to bar an adversary from approaching along a broad front.  These presumptions are reinforced by the second introductory paragraph from Mahan:

The same general principles apply to lines as to other intrenchments; but, from their great extent, they usually receive a slight relief, and the simplest angular figures are adopted for their plan.  In laying them out, the engineer should avail himself of all the natural obstacles presented by the position, so as to diminish the labor of erecting artificial ones.

See how this becomes counter-intuitive?  Complex entrenchments should, according to Mahan, be refined with simple angles of defense and fewer ancillary obstacles.  And from the perspective of the historian studying fortifications of the Civil War to latch onto.  Mahan feared exponential growth of labor requirements that might come from very complex arrangements.   And to that point, let me skip ahead to the last passage from the chapter on complex entrenchments:

Besides, a very capital objection in war, the time and labor required to throw up so many works are altogether beyond what can be disposed of in the ordinary circumstances of an army.

The emphasis is in the original –  “a very capital objection in war.”

You see, this is the point at which we must start reconciling what we know of field fortifications as a function of military science with what we know of the same fortifications as a described from wartime correspondence and observed with the surviving works.  Indeed, if one studies the accounts and walks along the surviving works, there are serious questions about how much of Mahan’s teaching shows up on the battlefield.  Sure, we see star forts, bastions, and redans at some places.  But how do we account for the entrenchments scattered about Virginia, particularly from the Overland Campaign?  (And mention Northern Georgia and a plethora of other places, but I’m selecting a handy point of reference here.)  The works at the Wilderness, Spotslyvania, and North Anna seem to be contradictory, in some places by small increments but at others with a wide gap, to Mahan’s teaching.

And this requires us, as historians, to recognize military science is not a fixed field of study.  Like any other profession, military science evolves, changes, and re-invents.  It is ever changing, even while reliant on core principles.  And with that in mind, we must lay Mahan’s pre-war teachings beside his post-war revisions, to the same manual of study.  Furthermore, we must also pull in the post-war manuals, such as Wheeler’s, which I much prefer, as additional perspectives.  It is vital to understand not only that military science was applied on the battlefield, but it also evolved due to its application on the battlefield.  We’ll see, as I progress along this thread of posts, how Mahan’s construct of “simple and complex” field fortifications would transition into Wheeler’s “simple, complex, and hasty” fortifications…. and that’s being overly simplistic.

There in lies the complexity when studying these complex entrenchments.  There is much a “point in time” to consider.  Not so much that manuals needed to be re-written, but that the re-writing was derived from experience derived from the very occurrences being studied.

I’ll go one further.  It is not enough that we recognize that military science evolved, offering a new approach to the application of field fortifications.  We should also seek out the drivers that caused that evolution.  Now we might lay this at the alter of the rifled musket.  But I’d challenge that long held belief a bit.  If this was all due to accurate, high-velocity projectiles, wouldn’t the natural evolution be towards thicker, stouter, more resilient works?

I say there’s more to it than just the mine ball and Hotchkiss shells.  And that something had to do with the point Mahan cited – time and labor.  In my opinion, the more important driver on military science were the advancements of technology that translated to better logistics and communications.  Those, by application, translated to operational mobility which far surpassed that of previous generations of warfighters. Then by extension, that gave the battlefield commander more resources to apply to the situation. You see, in order to add more complexity to those complex entrenchments, one must afford more time and labor.

OK…. I’m tipping my hand to a conclusion for which I’ve not presented the evidence.  To do that, we must first explore Mahan’s complex entrenchments, or lines, in detail.

(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, pages 69 and 75.)