The French mining attack on the Mastbastion at Sebastopol between
February and April 1855, launched from the third parallel about 190m from the
Russian ditch. Todleben’s countermines surround the Mastbastion. (From
Zschokke, Handbuch der militärischen Sprengtechnik (1911).
The French right attack gallery in the above plan, 0.8m high, has been
driven through a clay layer beneath hard chalk at a depth of about 6m but has
been broken by heavily overcharged Russian blows.
The attack of a fortress by mining is recorded in the ninth
century BC. A tunnel was driven beneath the walls and the soil replaced by
timber props, which were then destroyed by burning, causing the walls to
collapse. Mining was usually resorted to when artillery had failed and was a
slower, but ultimately more certain, method of reducing a fortress. In the
first century AD the Roman writer Vitruvius described methods of attacking
fortress walls. At ground level covered protection, such as a ‘testudo’, or
tortoise, was used against projectiles thrown from above to enable the walls to
be attacked with hand tools or a battering ram. Where mining was employed he described
the burnt-prop method to bring down walls and also the use of a tunnel to
emerge inside the fortress or walled town, from which attacking soldiers issued
to surprise the garrison. This technique was used by the Romans to end their
nine-year siege of Veii in 396 BC. Sometimes the knowledge that the walls of a
fortress were undermined was sufficient for the garrison to capitulate, as at
Marqab in 1285 when the Knights of St John surrendered after being shown the
extent to which Egyptian miners had tunnelled beneath their great tower.
Defences against mining incorporated into fortresses included ready-dug
countermines and a deep and wide water-filled ditch. A breach in the walls was
so often decisive in breaking a siege that in medieval times it became a
convention that the garrison of a castle or fortress might surrender with
honour once their walls were breached, whereas if they continued to resist
quarter would not be shown and the castle could be sacked.
In fifteenth-century Italy there occurred the only major
technological change in military mining from antiquity until 1914, when
gunpowder replaced the burning of props to bring down walls. This greatly
increased the power and potential of mining, as walls would now not just
collapse, but be hurled into the air along with the defenders. Gunpowder also
enabled miners to engage in warfare beneath the ground, attacking their
opponents’ tunnels by exploding charges, called camouflets, to collapse them,
which did not break the surface of the ground. The increased danger to the user
entailed by gunpowder saw the rise of regulations to cover mining and, during
the seventeenth century, highly sophisticated and standardized forms of
fortifications and the means of assault were developed. The French emerged as
the masters of siege craft, with the engineer Vauban the dominant figure. The
usual method of approach by the besieger was to dig a trench, known as the
first parallel, 600 to 700m from the fortification. This was at a distance far
enough away for the trench not to be enfiladed (i.e. fired along the length of)
by the defenders and earthworks were then thrown up in front for siege
artillery to begin firing. Under cover of these guns engineers began to dig
approach trenches, known as saps (hence the term ‘Sapper’ for a military
engineer), towards the fortress. These were in a zigzag pattern to reduce the
effect of enfilade fire. At about 300m from the fortress, a second parallel was
dug and new artillery emplacements prepared. From this range the guns could begin
to batter a breach in the walls. The defenders might attempt sorties to spike
the attackers’ guns. If the artillery assault was not successful, the besiegers
continued sapping forwards, by now under small-arms fire, to within a few
metres of the walls, or a ditch or moat surrounding the fortress, and
constructed a third parallel. If the artillery was still unable to smash gaps
in the walls, mining would begin.
A well-designed fortress incorporated a system of tunnels
surrounding its walls designed to detect the mines of the attackers, known as
countermines (the term ‘mine’ being used for both the explosive charge and the
tunnel from which it was laid). Camouflets would be used to destroy the
attackers’ mines, but the defenders were restricted in the size of charge that
they could use, for fear of destroying their own defences. The distance at
which a charge was likely to damage an opponent’s tunnel was known as the
‘radius of rupture’. Mines that were powerful enough to break the surface of
the ground to form a crater were known as ‘common mines’. The distance of a
mine from the surface, used to calculate whether it would break surface, was
the line of least resistance (LLR). To prevent the blast of a mine being
directed down the tunnel in which it was laid, the tunnel would be extensively
backfilled in a process called ‘tamping’. In the late seventeenth century
formulae for the sizes of charges were developed by Vauban and Mesgrigny,
followed by Belidor, who carried out trials in 1725. His calculations were not
accepted in France, but were taken up by Prussia and used at the Siege of
Schweidnitz in 1762, where the Prussians blew mines of up to 2,500kg. The
Russians gained much experience during the Russo-Turkish War in 1828 and at
Brailov fired two mines of 4,000kg, although with only partial success, as the
huge quantity of debris thrown up buried the junction box, preventing the next
set of mines from being blown and also ultimately hampering the Russian
advance. It was thus not just size that mattered: mines also had to be
coordinated with the attack. The Russians used this experience during the most
significant mining of the nineteenth century, in the Crimean War during the
Siege of Sebastopol. Against a Franco-British attack the Russian chief engineer,
General Todleben, organized a system of countermines and some twenty mines were
blown, varying in size from 550kg to 2,000kg. Mines were driven through a layer
of clay beneath hard chalk. Todleben discovered a second layer at about 15m
depth, which he used for a deep level system of countermines. He laid a charge
of 4,000kg, which was discovered after the fall of Sebastopol; at that depth it
would not have been great enough to break the surface.
Protracted siege warfare and mining did not, however, play a
major part in the Franco-Prussian War of 1870-71, during which the French
fortresses were forced to surrender through containment or powerful
bombardment. After 1870, the opinion of most artillery and engineer officers in
the great military powers was that long-range, large-calibre artillery, especially
mortars and howitzers with plunging fire, would always defeat fortresses that
previously could be breached only by mining.
By the 1880s it seemed that fortresses had become obsolete,
along with the ancient means of assaulting them. There were, however, opposing
trends. The Russo-Turkish War had involved a five-month siege of Pleva in 1877,
conducted by Todleben. During the American Civil War mining was used against
field works rather than a fortress at the siege of Petersburg. A 511ft gallery
was driven by the 48th Pennsylvania Infantry, which was both commanded by and
composed mainly of coal miners. The unit laid a charge of 3,600kg at 6m depth
beneath a Confederate earthwork known as Elliott’s Salient, which was blown on
30 July 1864. The mine killed 250 to 350 Confederate soldiers, but in the
resulting Battle of the Crater the Union attack was badly coordinated and many
of the attackers were trapped in the crater by a counterattack.
