Fortification Friday: Permanent or Field Fortifications?

Some time back, a reader suggested that I post about the various terms used to describe fortifications.  Sounded like a good idea, so let me kick off this first “Fortification Friday.”

For starters what is a fortification in the context of the Civil War.  Well the dean of fortifications, as far as the American experience goes – Dennis Hart Mahan wrote in his 1856 Treatise on Field Fortifications:

All dispositions made to enable an armed force to resists, with advantage, the attack of one superior to it in numbers, below to the Art of Fortification.

This means used to strengthen a position, may either those presented by nature, as precipices, woods, rivers &c., or those formed by art, as shelters of earth, stone, wood, &c.

Interesting here that Mahan pins the use of fortifications to the side with inferior numbers.  Fortifications were combat multipliers, enabling a handful of men to represent a strength beyond their raw numbers.  But does this mean Fortress Roscrans (the largest enclosed fort built during the war) or the Defenses of Washington during much of the war, where the garrison technically outnumbered any potential adversary, were simply “outposts”?  Perhaps at the strategic measure, but those fortifications were designed to allow a small force posted at points around the perimeter to hold off a deliberate, focused attack by a larger enemy force.  Or a better way to put it – a guard force on the perimeter could hold the enemy advance until the full force of the garrison arrived.

In his writings, Mahan further broke down the art of fortification into two disciplines – permanent fortifications and temporary (field) fortifications:

If the artificial obstacles are of a durable character, and the position is to be permanently occupied, the works receive the name of Permanent Fortification; but when the position is to be occupied only for a short period, or during the operations of a campaign, perishable materials, as earth and wood, are mostly used, and the works are denominated Temporary or Field Fortifications.

Clearly Fort Sumter and Fort Moultrie were permanent fortifications.  But Batteries Wagner, Gregg and those on Sullivan’s Island?  I’d argue those are in one sense permanent, since the intent was those works would defend Charleston for an indefinite period of time, despite the use of temporary materials.  In a revised version of Mahan’s original text on Permanent Fortifications, James Mercur introduced the permanent fortification:

The term permanent fortification is applied to those defenses which, constructed of materials of a durable nature, and designed for permanent occupancy by troops, receive such a degree of strength that an enemy will be forced to the operations either of a siege or a blockade to gain possession of them….

The object of such defenses is to secure the permanent military possession of those points, either on the frontiers or in the interior of a state, which must, at all times, have a well-defined bearing on the operations of a defensive or offensive war.

In that regard, Battery Wagner, Battery Gregg, and the additional batteries built on Sullivan’s Island were part of a system of permanent fortifications around Charleston defined to hold a coastal frontier.

Delineating the properties required of permanent fortifications, Mahan continued to list the conditions a defender must attain to properly setup these permanent defenses:

  1. Strength to resist open assault by ordinary means.
  2. Sustainable shelters to protect troops, armament, provisions, and magazines.
  3. Laid out so that all exterior points within range can be swept by cannon fire.
  4. Secure means of communication and movement of troops within the defenses.
  5. Configured to allow the defender to dispute any attempt to occupy, “every point both within and exterior to the defenses.”

In those measures, Battery Wagner was a failed, but flawed, permanent fortification.

But let’s go back to the force multiplier factor granted by fortifications.  Mahan considered the base element of the fortification, be that permanent or temporary, to be the intrenchment (I’ll stick to his spelling if for nothing else to annoy those pesky grammar-istas out there).  As he wrote in the 1856 Treatise:

The general appellation of Intrenchments is applied to all field works; and a position strengthened by them, is said to be Intrenched.

To enable troops to fight with advantage, the intrenchments should shelter them from the enemy’s fire; be an obstacle in themselves to the enemy’s progress; and afford the assailed the means of using their weapons with effect.  To satisfy these essential conditions, the component parts of every intrenchment should consist of a covering mass, or embankment, denominated the parapet, to intercept the enemy’s missiles, to enable the assailed to use their weapons with effect, and to present an obstacle to the enemy’s progress, and of a ditch, which, from its position and proximity to the parapet, subserves the double purpose of increasing the obstacle which the enemy must surmount before reaching the assailed, and of furnishing the earth to form the parapet.

So look at fortifications as the counter to both firepower and mobility.  A good Intrenchment would stop the enemy’s movement AND deflect his fires.  A fortification was the preventative applied against the enemy’s artillery. Or conversely, artillery was the direct solution to an intrenched enemy.  Keep that in mind when reading about the soldiers rapidly building field fortifications during actions from 1863 on.

As to the proper evaluation of a fortification’s value, in what we might consider doctrine today:

Intrenchments should be regarded only as accessories to the defense of a position. They are inert masses, which, consuming a portion of the enemy’s efforts, and detaining him in an exposed situation to the fire of the assailed, insure his defeat.

Let’s put emphasis on that last bit.  Mahan did not propose to his students (and you know who those were) that they stand their troops behind works to simply throw the enemy back.   No, he suggested an active defense.  The intrenchments were “accessories” that enabled the strong counter-punch.

Shades of some 20th century doctrine, perhaps?

(Citations from Dennis Hart Mahan, A Treatise on Field Fortification, New York: John Wiley, 1856, pages 1-2; and Mahan’s Permanent Fortifications, edited by James Mercur, New York: John Wiley & Sons, 1888, pages 1-2.)

Published by Craig Swain

"Historical marker hunter" and Civil War enthusiast.

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