American Civil War
Petersburg in Virginia was an extremely important waypoint for the Confederacy during the American Civil War, converging four railway lines before redirection to Richmond, the capital of the Confederacy. The railways were the greatest means of transport for soldiers and logistics at the time and as long as Richmond could gain supplies and reinforcements, the two armies were going to be held in a stalemate at the capital. The Union army knew that Petersburg could be used as a backdoor into Richmond and capturing the city would destroy the Confederate logistical supply lines, forcing the eventual collapse of the defending forces. The two armies remained deadlocked on the outskirts of both cities however, with the Confederates digging into the ground, building over thirty miles of trenches from Cold Harbor at Richmond’s east, down to the south of Petersburg, creating a scene very similar to what would be seen throughout most of the First World War. General Grant understood the issues brought about by a long siege and desperately sought an answer to end the battle quickly before his soldiers began to settle, but there seemed to be little that could be done. That was until Lt. Col. Henry Pleasants who was a mining engineer before the war, brought forward the idea of digging a tunnel underneath the Confederate defences and detonating explosives under them, forcing a hole through the centre of their lines.
Construction of the tunnel began on June 25th and when completed, spanned 510.8 feet long and rose to only twenty-five feet underneath the Confederate lines. At the end of the tunnel, two lateral galleries were then dug spanning around forty feet in both directions, however the right gallery was forced to curve further out as the tunnellers heard footsteps from above ground. Then fearing that a counter-tunnel was being dug or a gun platform was being constructed, Pleasants decided that he had to alter the construction plan. “Pleasants estimated that his men had excavated over 18,000 cubic feet of earth from the approximately 600 feet of tunnel”. Four magazines were dug in both of the lateral tunnels which were reinforced with timber planks as well as drainage systems after springs were discovered at the end of the main tunnel, resulting in the ground being wet and muddy. The strength of the tunnel walls was also of extreme concern as the recent heavy rainfall was expected to have compromised their ability to hold firm.
One of the greatest challenges facing the tunnelling operation from the moment it was mentioned was the question of how such a tunnel could be ventilated. “400 feet was the maximum length for such a tunnel without external ventilation tubes, which had been proven at the siege of Lucknow, in India.” Mines were typically ventilated through the construction of vertical shafts reaching the surface. These shafts would be placed every few hundred feet throughout its length, but such shafts could not be constructed because of the practicality of the operation. Pleasants’ suggestion was to construct a single vertical shaft which would be dug into the tunnel wall near its entrance with a constant fire burning at its base. The entrance would then be sealed off using airtight burlap, allowing the fire to suck the used air out of the far end of the tunnel. An eight-inch square wooden air duct would then be built into one of the bottom corners of the tunnel that would be continuously extended as the tunnel is dug, creating a constant air flow throughout its entirety.
Figure 2. Sketches of the Union armies’ tunnel at Petersburg.
While Pleasants men never met any challenges from Confederate counter-tunnelling operations that resulted in any issues, there were operations in place that aimed to find and destroy the Union tunnels. Edward Porter Alexander was the Chief of Artillery in Petersburg and made it a routine to scout the Union trenches in an attempt to anticipate their next move, and on June 30th, he discovered that the Union army were attempting to tunnel their way under the Confederate lines. Alexander informed General Lee of what he had uncovered and after much debate, the Confederate’s began work on their counter-tunnelling operation. Standards were much different to the Union operation however and the Confederates began work on five tunnels in order to locate the Union works, but with such a lack of equipment, were forced to carry dirt out in cracker boxes. In order to conceal the tunnels, they were dug behind the forward trenches and then dug underneath them, where they would turn left and right, almost parallel to the trenches. Similar problems faced the Confederates as the Union tunnellers in terms of digging the earth, with it being a mixture of soft clay and sand, making the tunnel walls and roof far less sturdy and in need of heavy support.
“The main… passageways, were generally cut four by six and framed up every four or five feet with four by four square timber frames, one-inch plank slipped in on top and often on the sides. Another plank on the floor served as a wheelbarrow runway.”
The Confederate attempts to stop the operation ultimately failed with the Union army detonating the packed in explosive on July 30th before sending in an infantry assault on the newly created gap in the Confederate lines. The crater left behind was said to have measured “200 feet long, 70 feet wide and over 30 feet deep”, killing around 278 men.
“The noise of the explosion was a dull, rumbling thud, preceded… by a few seconds’ swaying and quaking of the ground in the immediate vicinity. The earth was rent along the entire course of the excavation, heaving slowly and majestically to the surface, and folding sideways to exhibit a deep and yawning chasm.”
The Union failed in their assault however, with their soldiers running straight into the crater and unable to escape, allowing the Confederate soldiers simply having to stand above them and pick them off. The re-enforcements sent in to alleviate the first assault ended up making the same mistake in the chaos of the gunfire and smoke, getting caught in the crater and meeting their demise.
This extract has been taken from my Dissertation Subterranean Warfare: From Crimea to WW1, written in Carlow College St. Patricks in 2022 under the supervision of Dr. Ida Milne.
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