Fortification Friday: Mines! The exploding obstacle.

The last sort of obstacle described by Mahan in regard to field fortification was the mine.  The word “mine” is itself rather quirky when applied to military science.  The word use is arguably consistent, in that a mine is a concealed explosive device.  However, through the centuries the physical form and functionality of the mine has varied.  Furthermore, in the Civil War context, the term “torpedo” applied to many sorts of “mines”.  Thus we have another term which should be understood in context.

When we say “land mine”, to be specific to field fortifications, now days we think of something like this:


The idea is to bury or other wise conceal this sort of weapon in a location that the enemy might use as a avenue of approach. This particular Chinese mine is typical of modern types, in that it has a trigger.  Once in place, it does not require involvement of the defender.  Just an unlucky attacker (or innocent civilian as happens too often) to trigger the weapon by movement or influence.  There are scores of variations used for triggering and detonation – trip wires, magnetic influence, motion detection, simple pressure plate, and such.  And there are several different variations regarding what the weapon does when triggered, based on the intended effect – anti-personnel or anti-tank being most frequently cited.  Of course, we know of “torpedoes” that were used in this manner… well, not anti-tank of course… during the Civil War.

However, not all mines are triggered by the attacker’s missteps.  Other types are designed to set off at an opportune moment by an operator.  Command detonated is the phrase often applied.  This may be done via electrical signal or some sort of time fuse.  And please understand such mines could be used by the attacker as well as the defender.  The Petersburg mine is a famous example of a command detonated mine used for offensive needs.  But we’ll deal with the mine in siege operations at a later post.

Mahan was familiar with command detonated mines in the pre-Civil War days.  Even if he was not high on their use:

Mines. Attempts at applying mines to the defense of field works have seldom proved successful, owing to the rapid character of the assault, from which the mines are usually sprung too soon or too late; so that the only effect that can be counted upon for their use is the panic they may create.

In addition, let us consider setting off explosive devices in close proximity to defensive fortifications might well undo those structures.  So the defender had to be wary about placement.  And if placed too far from the works, the mine was of little use to break up the attack.  Worst case scenario, a mine would create a crater from which the enemy gained purchase near the works.  All considerations that spoke against the use of mines for most situations.

But that is not to say all command detonated mines were discouraged.  Mahan felt one specific employment had merit:

There is one species of mine denominated a stone-fougasse, which it is thought might be successfully applied to the defense of the ditches and salients of field works. To make this mine, an inclined funnel shaped excavation is made, to the depth of five or six feet, at the bottom of the funnel a box containing fifty five pounds of powder is placed, with a powder-hose communicates.

Technically speaking, the fougasse was considered an improvised mortar.  In its original form, the fougasse was a hole in the ground in which powder and the desired projectile payload was set.  The stone-fougasse was simply an evolved form.  Let me offer the accompanying illustration from the Mahan’s post-war manual, as it is clearer in detail:


As you see from the caption, we have four major elements.  The powder box itself is indicated by A and A’.  Mahan described the desired structure as “A strong shield of wood, formed of battens well nailed together” and placed in front of the box.

In front of the shield over the powder is a pile of stone, marked B and B’.  These would be “three or four cubic yards of pebbles, or an equal weight of brick bats, or other materials….” Note the suggested dimensions of the funnel in front of the pile – 22 feet out and an 18 foot mouth.

The powder-hose is indicated by C and C’.  Lastly, D and D’ are, in the original text, a “powder trough tamped with sand-bags, which, with the arrangement of the earth, as shown in the section, are to prevent the load from acting to the rear.”   That being a good thing for the defender, serving to reduce damage of the works in close proximity to the stone-fougasse.

Mahan suggested, “A fougasse of this size, when sprung, will scatter pebbles over a surface sixty yards in length, and seventy yards in breadth.”  Such would do great injury to an attacker confined in the ditch or exposed in front of a salient.

Writing post-war, Junius Wheeler offered a variation on this theme:

Shell-fougasses. – A shell fougasse is a box containing loaded shells, concealed in the earth, and so arranged as to be exploded when the enemy is over the spot.

The box is divided by a partition into two parts, an upper and a lower. The loaded shells are placed in the upper part, with the fuzes downwards and connecting with the lower part by holes bored in the partition.

A charge of powder is placed in the lower division of the box of sufficient quantity, when fired, to throw the shells to the surface.  This charge is fired by means of a fuze, or electricity, like other fougasses.

Again, a nasty prospect for attackers.  But as with the caveats offered by Mahan, the defender had to take care when placing this or any other command detonated mines.

Before leaving the command detonated mines, allow me to connect two modern-day variations on the theme.  First off, command detonated mines are still used by modern armies – most notably the M18 Claymore Mine:


We see here the mine itself, marked “Front Toward Enemy.” Inside the plastic case is an explosive.  And in front of that explosive is a layer of steel projectiles.  So very much a miniature version of the stone-fougasse.  Also seen here is a spool of wire and a trigger mechanism, which also relate to elements Mahan described for his fougasses.  The optimum range of the Claymore is about 55 yards.  So we see the concept remains practical, but is much more refined.

And fougasses themselves remained in use by military forces right up to modern times.  Through the 20th century, several variations were applied.  The most often seen variation replaced rocks, shells, or other projectiles with flammable liquids:


The French being corrupted to “foo gas” by soldiers in some cases.  But you see the same basic elements of Mahan’s fougasse.  And the intended method of employment is very much the same as in Mahan’s day.

Before leaving the discussion of obstacles, let us exceed Mahan’s “lesson plan” a bit and discuss that other type of mine… called torpedo in Civil War texts… in the next installment.

(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, pages 49-50;  Mahan, An Elementary Course of Military Engineering: Part 1: Field Fortifications, Military Mining, and Siege Operations, New York: John Wiley & Son, 1870, page 78;  Junius B. Wheeler, The Elements of Field Fortifications, New York: D. Van Nostrand, 1882, page 181.)


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