Fortification Friday: Big magazines…as used around Washington

There is a tendency to characterize the practice of military science as seen during the Civil War as somewhat stagnant.  The generalization is the generals were fixed of mind towards Napoleonic tactics and strategy, insisting linear infantry formations be thrown into battle as that was “the right way” to do things. All the while, of course, technology advanced to render such tactics obsolete and the battlefield more lethal.

But as one examines the practice in more detail, the characterization appears far less static, and in many ways innovative.  What should be clear is how Civil War leaders appreciated the lessons from the battlefield.  They used practical experience, which could only be derived from actual wartime situations, and applied such to future activities.  Going into the post-war, many of those lessons learned became part of the teachings imparted to junior officers.

A example of such, though arguably minor, appears in our discussion of magazines.  And it comes directly from the old sage who taught all those supposedly wooden-headed, would-be Napoleons at West Point – Dennis H. Mahan.  Writing in 1870, Mahan offered these observations about bomb proof magazines:

Bomb Proof Magazines. For field works of a semi-permanent character which are to be indefinitely occupied, have an armament of heavy guns, and are expected to stand a siege, like the defenses around Washington for example.  The magazines, bomb, and splinter proof shelters, should be constructed of the heaviest timber, and be covered securely with earth from the assailant’s curvated and direct fire.

Sure, at first glance just another description of the need to build a structure to resist enemy fires.  But consider the language in detail.  Starting with the notion of “semi-permanent” fortifications.  Such alludes to a practice not fully appreciated prior to 1860.  The US Army’s way of waging war in the antebellum focused on two modes – garrison and field.  Garrison implied permanent, established facilities, such as nice masonry fortifications with well protected magazines.  Field implied temporary facilities that were only expedients between campaign movements.  The US Army didn’t plan for things in between those modes. However, in practice during the war, there were many more situations where semi-permanent was the mode.  And facilities of those type were often required to stand in the threat of enemy pressure… be that a short-duration raid or deliberate siege.  (Not saying here that sieges of such places were common, but rather those designing the semi-permanent facilities considered that in the requirements.)

Another language detail – “heaviest timber.”  Not scantling, facines, or planks.  Rather heaviest timber!

And the word to really pay attention to here – “curvated”… as in high-angle fires.  Can’t stress this enough, particularly after the summer of 1864, armies employed high angle fires more and more – going from artillery acting on the horizontal plane to on the vertical plane; having projectiles plunge down on the target, instead of attempting to batter the target down directly.

And of all the facilities constructed during the Civil War, those around Washington received the most attention, and were best documented!  So we see Mahan choosing those as the example to follow.

As Mahan continued, we see more emphasis, than offered in the pre-war text, towards ventilation and drainage of the magazine:

The ventilation of the magazines and precautions for their drainage, are of the utmost importance.  Fig. 40 and 41 give the plan and a cross-section of a magazine constructed in a work of this character.

And here is Figure 40, showing the plan:

MahanFig40 And Figure 41 with the cross-section:  MahanFig41

Note the construction of dedicated ventilation pipes.  Also note the peaked (vaulted?) ceiling.  We will return to those in a moment.

Mahan continued to describe the construction:

The sides of the interior of the magazine are formed of twelve-inch logs placed vertically in juxtaposition and resting upon a ground-sill.  These are capped on top by a two-inch board, a strip of a like kind being spiked on within the cap.  The top is formed of fifteen-inch logs, also in juxtaposition, each having a shoulder of three inches to fit it to the cap and inside strip.  Longitudinal logs are laid on these with varying diameters, so as to give a proper pitch for the roof.

We’ve gone from six-inch scantling, for the coffer-work magazinefor the coffer-work magazine, to twelve-inch logs for this semi-permanent bomb proof.  And for this context, juxtaposition implies very close fitting, as opposed to some odd, contrasting arrangement.  And with that, the walls and other interior arrangements could be set:

Earth is solidly packed upon the top and between the roof logs, receiving the proper slope for the roofing boards.  These boards, carefully jointed, are laid on in two thicknesses, each being covered with a coating of asphalte.  The flooring of the magazine is of joists and boards.

Far more elaborate than the earlier magazines, to include a coating of asphalt to reduce water seepage.

Now back to the ventilation arrangements:

The sides of the magazine are surrounded with an air-chamber formed by inclined logs supported on a ground-sill and resting against the top logs; these are placed at three or four feet apart, each one being braced at the middle point to resist flexure from the pressure of earth.  The chamber is covered in by saplings laid in juxtaposition. There are ventilators between the magazine and the air-chamber near the top, and also between the later and the external air; the two not being opposite, and the usual precautions to guard against accidents from sparks being taken.

So it was deemed more important to provide ventilation pipes through the structure, despite creating a potential weak spot in the magazine.

With these arrangements complete, time to pile on earth to render the structure bomb proof:

The earth-covers is ten feet on the exposed side, and six feet on the other sides and on top.

In the pre-war text, Mahan had not directly stated the thickness of earth required. In part, this was to be regulated by the amount of space within the work.  Clearly the magazine being subordinate to the needs of batteries and other interior arrangements.  But post-war, we see a specification in feet for the thickness.  Something implied here.  What good are fine, well-spaced batteries if the magazine is blasted to shreds?   Must pile that earth to proper thickness and resist rifled projectiles!

Lastly, we need a doorway to reach the magazine:

The entrance to the magazine is well secured by a bomb proof covering.  A slope is given from the interior to the foot of the steps leading to the level of the floor for the purposes of draining.

Recall in the pre-war text, Mahan specified a splinter proof covering.  Post-war that was upgraded to bomb proof.  Notice that in order to achieve a bomb proof “rating” for the example given, we have a sharp turn built into the entrance-way.  This served to cover the entrance more completely and also to block errant splinters or sparks.

What we’ve seen with these paragraphs describing bomb proof magazines is the result of field experience applied to teaching the next generation of officers.  During 1861-5, the military found out there was a need for something more permanent than field fortifications, yet not as deliberate as permanent, garrison fortifications.  And those semi-permanent works, covering vital subjects such as the nation’s capital, required stout bomb proof magazines.

They also required similarly bomb proofed shelters for the men inside the works.  That’s next!

(Citation from Mahan, An Elementary Course of Military Engineering: Part 1: Field Fortifications, Military Mining, and Siege Operations, New York: John Wiley & Son, 1870, page 52-4.)