Fortification Friday: shot proof, bomb proof, splinter proof… those are not the same!

In the discussion of magazines thus far, I’ve contained our examination to Mahan’s pre-war instruction on the matter.  However, we should all recognize, from reading wartime reports, the use of the descriptions shot proof (shot-proof, or shotproof… you grammar enforcers need to sort out which is proper), bomb proof, and splinter proof.  Earlier, I pointed out that Mahan specifically used the term “shot proof” when defining powder magazines … in the context of field fortifications:

Powder magazines. The main objects to be attended to in a powder magazine are, to place it in the position least exposed to the enemy’s fire; to make it shot proof; and to secure the powder from moisture.

Let’s focus on these three terms (my definitions here):

  • Shot proof:  Possessing the ability to arrest or at least divert the trajectory of solid shot.  Preferably arrest the solid shot, leaving it embedded on the works or harmlessly bounced to the ground.  Ricochets were fine, but might be dangerous elsewhere in the works.
  • Bomb proof: Able to prevent damage due to shells.  Keep in mind the shell that embeds and explodes will cause more damage than one glancing off and exploding. So there are some desired properties that run contrary to the same structure being rated “shot proof.”
  • Splinter proof:  Has sufficient resistant qualities to arrest the trajectory of fragments from a shell.

Purist might also add structures designed to stop musketry.  True, but for now let us focus on that used to build magazines.  Thus we see three different … shall we say… ratings for defensive structures.  Each with different qualities and requirements.  Furthermore, prior to the war Mahan did not give much discussion about sheltering troops, equipment, or materials, other than the ammunition to be stored in magazines.

I think these are important hairs to be split.  Mahan retained the same definition for powder magazines in his post-war version of the text.  And simply repeated the same remarks about construction of such.  But, at the end of that section, he added the following:

The magazines here described, are only suited for works which are not expected to be occupied but for some weeks and are not exposed to attack of any but light field guns.  In all cases where lumber is abundant, it will be best to cover at top by a foot in thickness of pieces laid in juxtaposition, and to give a covering of at least six feet of thickness of earth on the most exposed side, and place the magazine entirely underground.

Skipping a paragraph on wartime splinter proofs (which we will return to later), Mahan proceeded to introduce by name the bomb proof magazine:

Bomb Proof Magazines. For field works of 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.

Notice here Mahan insists the bomb proof magazines need possess the ability to resist direct and indirect fire (which he called curvated).  And offered this figure as a suggested profile of the bomb proof:


We are going to examine this structure in more detail, but for now I want to focus attention on the front (right) side.  The diagram demonstrates as slope of 35°. On the interior side (left), we see a slope of 45°.  Thus the side not facing the enemy would retain the natural slope – that 45° slope at which the engineer would expect the pile of dirt to sustain itself against the force of gravity – while the side facing the enemy would have a gentler slope.  In fact, that front side has a slope just a bit greater than that preferred of the parapet.  This not only increased the chances of a projectile glancing off as a ricochet, but also improved the relative thickness of the magazine’s protective cover.  A World War II analogy is apt here – sloped armor of the T-34 tank as opposed to the straight sides of the Panzer IV (or early Tiger tanks).  Sloped armor… and sloped earth… is more resistant to projectiles.

Mahan does not dwell on the nature of this change.  We might easily speculate on the nature and improvement of rifled projectiles by the end of the Civil War. But I would call out another important shift in the practice of artillery fire by 1864.  That is more emphasis on indirect… curvated, if you prefer… fires.  As discussed during the sesquicentennial, the use of mortars, field artillery firing as mortars, and other forms of high-angle fire changed the battlefield.  (Though, sadly, this is a point lost on most historians who have explored the matter… as they rush to discuss rifled musketry and soldiers digging foxholes…..)

So we see one of these hairs – the differences between shot, shell, and splinter proofing – became rather important as Mahan re-assessed the practice of field fortification after the Civil War.

As to that other “hair” to split, Mahan also added, in his post war writings, a section on what he then termed bomb proof shelters.  Junius Wheeler, writing even later and when the lessons from the Franco-Prussian War were being digested, went one step further.  Wheeler actually subordinated magazines as a form of interior shelter.  Wheeler further reduced the ratings of these structures for simplicity:

Shelters. – An efficient defense of a field work is greatly aided by shelters, arranged for the men and the stores, so that the men can rest in them, and the stores be kept safe from the enemy’s fire.

Shelters are generally known as bomb-proofs, and splinter-proofs, which differ from each other only in capacity and strength.

Bomb-proofs must be strong enough to resist the effects both of the impact and the explosion of the projectiles which strike them.  They should be roomy, and when used by the men, should be well ventilated.

Splinter-proofs are so placed that they are not exposed to the impact of projectiles.  They are liable to be struck by fragments of shells, or splinters knocked off by the impact of a projectile, and are therefore made only strong enough to resist the effects of flying fragments and splinters produced by shells bursting, or by projectiles striking near them.

So now the emphasis is beyond just protecting the ammunition.  We see that emphasis expanded to include force protection!  Further demonstrating this shift, Wheeler considered magazines to be, “Shelters in which the ammunition and other stores can be placed and kept safe from the effects of the enemy’s fire….”   And also note that Wheeler collapsed shot proofing into shell proofing.

Why the shift?  Again, I say it is due in large part to changes in the practice of artillery fire.  With more use of vertical (or better labeled, high-angle) fires, the defenders had more need of overhead cover.  No longer could the defender simply hide behind a breastwork, but now had to worry about shells bursting overhead or dropping into the works.  This is not to say high-angle fires were “invented” for the Civil War.  Indeed, the mortar… nay… we can go back to trebuchets if you want… were in use centuries before the Civil War.  Rather, we see by 1864 the confluence of practice and technology (namely improved fuses) that allowed gunners to use high-angle fire with increased effectiveness.  Though… we should point out… not nearly as effectively as the gunners of 1916-18… when artillery was really the bully of the battlefield!  And… by no coincidence, it was at the same time we see the art of field fortification on display, using the French countryside as a canvas.

(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, pages 58-9;  Mahan, An Elementary Course of Military Engineering: Part 1: Field Fortifications, Military Mining, and Siege Operations, New York: John Wiley & Son, 1870, page 52;  Junius B. Wheeler, The Elements of Field Fortifications, New York: D. Van Nostrand, 1882, pages 135-6, 139-40.)



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