The Siege Mortars and Their Related Skills during the Napoleonic Era
By Marc Morillon
Drawings by Pierre Salamand
Translation from French into English by Paul Morillon
Some of you have probably noticed in "la Cour d'honneur des Invalides", some strange "guns" with a short and wide tube. Those artillery pieces are never worked out by modelers who, by the way, ignore most of their roles and functions. These devices, have nevertheless been extensively used during the sieges of strongholds during the XVIII and XIX centuries. For the First Empire period, which will be our focus now, this materiel deserves to be better known and represented. It has undoubtedly been much more employed in the field than some others which, even though popular, are almost theories such as the well known "Wurst" belonging to the medical services .
The originality of these artillery pieces lays with their projectiles: the bombs.
Cannonballs, solid projectiles, fired by the ordinary field artillery pieces along a straight alike trajectory.
So the bomb was a hollowed sphere, which inner surface was reinforced in its bottom (culot in French) whose role was to sustain the burst pressure. However, there was always the danger that the projectile would explode soon after departure, in which case the artillery piece could be damaged or destroyed. Every bomb was equipped with a fuse, a hollowed pipe made from a lime tree and filled with an inflammable mixture, which length and density were "estimated" by the artificer.
The powder load (we would say the military head today) could also be adjusted to put the emphasis more on the incendiary effect or on the lightening effect for instance. Every bomb was equipped with 2 rings passing through "ears". Those rings eased the transport of the particularly heavy projectiles, with the help of levers and S shaped hooks.
Their look is typical: the tubes are short and huge: calibre reaching 200 to 300 mm. The carriages are bulky; in fact these are sorts of bases able to sustain the almost vertical propelling burst, being understood that the firing angles ranging from 45 degrees, as a minimum, to 60 degrees, the most frequently used. The whole lot, extremely bulky, weighted depending on the calibre, 1500 to 2500 kilos.
There were several types of tubes used during the Napoleonic Wars:
Tubes with cylindrical chamber, in service at the beginning of the wars with the Gribeauval system (the chamber was designed for a 1 to 2 kilos propelling charge!). With this system, the bomb weight was irregularly distributed in the mortar bore, leaving a gap of about 3 to 4mm with the inner tube, "the wind". One can easily figure out that, in these conditions, the bomb knocked against the inner tube when fired, and that, as a consequence, the tubes were quickly damaged. One artillery piece could fire 48 bombs within 24 hours, but it was wise to limit this rate to 30 to avoid damaging the mortar even more quickly.
To alleviate this disadvantage, the Knight of Gomer, artilleryman and friend of Gribeauval, had conceived truncated cone alike chambers. Therefore, the bomb was laid on a circular fulcrum and was centred. It was also boosted with a more regular thrust around its surface, which provided a fire power enhancement. These "modern" mortars were built from 1791 on.
Let's note finally that some archaic models survived in fortresses, such as the spherical chamber mortars known since the end of the XVII century. Such pieces were still used during the Napoleonic wars. In that case, those were mortars with bases which tube was solid with the carriage and therefore had a fixed tangent scale. They were employed for the defence of fortresses, along the sea coasts, and by the Navy.
Mortiers du Système Gribeauval
The gun crews were composed of 5 men. In 1808, one 6 inch mortar type, with a 3 men crew was added to the list. There was also an 8 inch mortar, outside the Gribeauval system. For these small calibres, the bombs could be loaded by one single man and the hooks were not needed.
Firing: until the mid XVIII century, the ignition was twofold. The ignition of both the fuse on the top of the bomb, and the propelling powder, required two igniters. One can imagine why this procedure was not only not convenient but also dangerous. Artillerymen then realised that the ignition of the powder contained in the chamber could set fire to the fuse under the condition that some space was left along the inner tube to enable the fire to communicate. This condition was fulfilled when the bomb was steadied with stocks along the inner tube and therefore saved a space, the "wind" to enable the ignited gas to bypass.
Firing the Gribeauval Type Pieces
According to Manuel de l'Artilleur the following were the procedures for firing the 10 and 12 inch mortars:
Preparations for Loading
The careful reader will have noticed the presence of some strange tools:
The broom: one can easily imagine that when the bomb was fired, incandescent powder pieces fell down on the wooden platform. Under these conditions, handling lightened portfires and powder was dangerous. One gunner was therefore tasked to sweep the surroundings immediately after each bomb departure.
The Bombardier's long cuffs: this man had, amongst other tasks, the critical responsibility to centre the bomb and to chock the stocks. Therefore he had to protect his sleeves when manipulating inside the inner tube.
Bomb's hook: only used for 10 to 12 pounds bombs.
Firing the Mortar
The following commands were given to fire the mortar:
"Front" Everybody faces the mortar.
Towing and Moving the Mortars
It is easy to figure out that this type of equipment, extremely heavy and without wheels, was difficult to move. For long distances they where mixed with the siege teams, equipped with the tremendous 24 pounds' guns, designed to breach down walls. Special harnessing were used. Tubes and carriages were transported together or separately, depending on their weight, on "mortar lorries", 2 wheeled vehicles, towed by 4 horses in single file. These transport dispositions were also of more practical use for moving within the trenches during besieging operations. The unloading was done by tipping out the lorry. Putting the gun on its carriage required lifting crabs. The bombs were transported in ammunition carts, trailer typed vehicles with rails. One could also use smaller means: cannon balls carts or even bombs' hand-barrows, which were similar to stretchers.
We have seen that most of the systems in use during the Napoleonic wars were relatively outdated, and therefore some tentative improvement were undertaken. The Peninsula War and in particular during the siege of Cadix (which lasted for more than 2 years) spurred the creativity of two artillerymen. Sénarmont and Villantroys explored the way to build long range mortars. Those almost revolutionary devices were used with variable success, but that is something for another article.
Le Blond, M. L'artillerie raisonnée Paris; 1761.
Duturbie, T. Manuel de l'Artilleur Paris An III de la République.
Aide mémoire des officiers d'Artillerie Paris; 1809.
Les canons de Valmy Booklet by the National French Army Museum (Les Invalides).
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Placed on the Napoleon Series: February, 2000
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