'Burglar's Plan': Storming The Fort Hill Crater
Poliorcetic art from Vicksburg, 1863
Alfred Edward Mathews, an enlisted soldier of the 31st Ohio Infantry Regiment, created this lithograph the same year as the bloody assault it depicts. He witnessed the very first siege mine ever detonated in North America to create the breach. It is a striking view of how “trench warfare” emerged during the 19th century industrial revolution — a kind of transitional fossil, a primary source account of the mass fire revolution, when positional battles started to resemble sieges.
Prominent in the foreground is the approach sap, a feature of siegeworks since ancient times that reappears throughout Western Front historiography, for example. Andrew A. Hickelooper, a captain and fellow Ohioan, even prepared overhead protection against hand grenades, part of which is visible on the center-left of the image. Shooters fire from parapets made with boards and gabions, bundled twigs filled with dirt. A siege technology at least as old as gunpowder, this shooting gallery is called a gabionade.
On the right, a raised gallery; on the left, a sunken one. The idea is to make the Confederates inside the earthwork fort keep their heads down, nullifying their height advantage. Otherwise, the defenders would stand atop the ramparts and deliver a plunging fire on the assaulting party.
Earlier sieges of the gunpowder age probably looked like this, too. Eurasian armies had stormed mines and breaches even before gunpowder, and its introduction merely professionalized military engineering. So when the American Civil War began, combatants already had a fully-formed idea of how to do this sort of thing. The occasion had simply never presented itself in the New World, yet.
Known to the Confederacy as “the Gibraltar of the Mississippi,” Vicksburg was the south’s final defensive foothold on the most important logistical corridor in the United States at that time. Maj. Gen. Ulysses S. Grant had systematically established Union dominance across the navigable watershed of the Mississippi with gunboats when he laid siege to Vicksburg. As the city’s nickname implies, geology and time created a promontory overlooking the river. Confederate cannons could damage even ironclad gunboats with plunging fire from the bluffs overlooking the water.
The decision to dig a mine under the 3rd Louisiana Redan, as the Confederates called it, or Fort Hill as the Union men titled the earthwork, came only after weeks of fruitless probing and a failed general assault. Designed by Maj. Samuel Lockett, a West Point graduate, the ramparts shrugged off bombardment with cannons and 20-pounder Parrott shells. “Fort Hill is said to be the key to Vicksburg,” wrote Wilber F. Crummer of the 45th Illinois. “We have tried to turn this key, and have as often failed — in fact, the lock is not an easy one, but we soon shall try the burglar’s plan, and with the aid of powder blow up the lock to ‘smithereens.’”
Earth history mattered again here, for the mine was to be dug out of the local loess soil built up from eons of Mississippi River silt. Reknowned for its fertility, this dirt is so conveniently stable when cut that Hickenlooper and his staff deemed the usual safety measures of shoring and bracing a military mine unnecessary. His proof was in the sheer bluffs overlooking the river that made Vicksburg such a hard target for the Army of the Tennessee and their gunboats. Made of any other dirt, they would crumble.
Federals dug “one thousand five hundred feet” in “less than thirty days” to reach the objective on 22 June 1863. The next morning, undermining began. Hickenlooper was not a professional engineer, but he was a careful planner and a good leader. Imposing strict counterintelligence measures to hide the entry point of his tunnel, Hickenlooper executed a textbook attack. Titled Logan’s Mine, it branched into galleries, ending in chambers, underneath the point where Hickenlooper’s approach sap ended. The chamber spaces were crammed with gunpowder, the branches and galleries backfilled with excavated dirt, the tunnel mouth stoppered so that the blast of the mine would be directed upwards and, Hickelooper reasoned, outwards, such that a happy breach formed in the ramparts for a Union force to enter.
Diggers could hear enemy countermining, “the conversation and pick-strokes of the Confederates” working from a vertical shaft inside the fort aiming to collapse the mine. The Union soldiers quit their work and evacuated for fear Logan’s Mine would cave in at any moment. Hickenlooper personally led them back inside, redoubling the pace of work and risking his own life along with his men.
They won their race in the early morning of 25 June.
After the war, Hickenlooper would write that “the soil of this locality consisted of a peculiarly tenacious clay, easily cut, self supporting, and not in the least affected by exposure to the atmosphere, thus rendering bracing and sheathing unnecessary.” He was not alone in this estimation. Frederick E. Prime and Cyrus B. Comstock, engineers in the Army of the Tennessee, wrote that due to “the compactness of the alluvial soil, lining for mining galleries [was] unnecessary,” as “these galleries were formed with ease.”
Logan’s Mine, Hickenlooper could brag after the victory, was “the first one of the war, and one of but two mines of any importance successfully fired during that unpleasantness.” He had reason to be proud, being first. But he was apparently working from a mine engineering guide that admitted its own ignorance about the science of soil and explosive blasting.
Dennis Hart Mahan, the author, had a small experimental evidence base from student tests on the campus of West Point. He had never tested gunpowder mine charges in the loess soil of the Mississippi Delta. Calculating from “pseudoscience,” as Steven E. Woodworth and Charles D. Grear term Mahan’s manual in Vicksburg Besieged, a 2020 academic history of the campaign, on the morning of 25 June Hickenlooper “deposited 1,500 pounds of powder in three different branch mines (500 in each), and 700 pounds in [the] center; 2,200 pounds in all,” by his own account. Informing his superiors that the mine would be ready to detonate at 3 pm that same day, Hickenlooper was exhausted from working in the languid summer heat. He would have no rest.
To support the assault, “Grant ordered a general bombardment all along the Union line for approximately fifteen minutes immediately after detonation,” Woodworth and Grear write. “Union commanders were to place their troops in the rifle pits and trenches along their respective fronts at 2 p.m. and, with the sound of the mine detonation as their signal, were to unleash a hailstorm of iron and lead against the Vicksburg defenses.” Best laid plans, etc.
Col. William E. Strong of the 12th Wisconsin helped Hickenlooper light the fuse to detonate the mine. “We crept forward together on our hands and knees from the terminus of the covered way,” Strong recounted, “and fired the dozen strands of safety fuse; and how coolly yet eagerly Hickenlooper watched the burning grain until it reached an embankment, and how we hurried back to ‘Coon Skin Tower,’ and held our watches and counted the seconds! All was quiet along the entire line from right to left, save a shot at long intervals from some wary sharpshooter on the other side.”
But the fuse took a half-hour longer to burn than anticipated, an ill omen. Hickenlooper agonized at his post. Federal troops began to mutter and wonder. Then, as Strong would relate after the war, “the huge fort, guns caissons, and Rebel troops … were lifted high into the air; a glimmer, and then a gleam of light — a flash — a trembling of the ground beneath our feet, and great clouds of dense black smoke puffed up from the crater of the mine, like jets from a geyser!”
Hickenlooper said “the whole Fort and its connecting earth-works appeared to be gradually moving upward, breaking into fragments, and gradually presenting the appearance of an immense fountain of earth, dust and smoke, through which one could occasionally catch a glimpse of dark objects, men, gun-carriages, shelters etc.”
Witnesses to the event were plentiful. “About half-past three,” a soldier in Gen. William T. Sherman’s command recalled later, “the parapet was seen to heave, and instantly up rose a huge dark column of earth, mingled with timber, tools [and] bodies of men, in the center of which for a second gleamed a lurid flame wreathed in white smoke.”
Then right away, “as if they were all pulled off by one lanyard,” union guns opened a steady fire on the defenses of Vicksburg. Serving in the 31st Illinois, William S. Morris wrote that the sudden bombardment produced overpressure, and “blood spurted from the nose and ears of the men at the big guns. Some put their hands to their ears; the sound seemed to penetrate the brain.”
As the smoke cleared, however, the “volcano” in the middle of the “Queen of Vcksburg” was revealed to be narrower than planned, for Hickenlooper had quite overcharged the mine, so that the firm soil had channeled the massive blast straight up into the sky, forming a conical crater rather than a collapsed one.
“Although there is no definitive proof that Hickenlooper used Mahan’s equation, Woodworth and Grear write, “the resulting crater, with a line of least resistance of twenty feet and a radius of twenty-five feet, suggests that the Seventeenth Corps engineer overcharged his mine” consistent with Mahan’s formula.
Hickenlooper recalled that “the explosion had destroyed about one-half of the redan and made of it an inverted cone-shaped crater about fifty feet in diameter and about twenty feet deep.” As seen in the lithograph, “the inner rim” of the crater “consisted of a parapet made by the descending earth.”
Storming this breach, the Federals discovered that the defenders of the fort had constructed an interior defensive berm around the area where they expected the mine to detonate. Now the Confederates “brought a battery into position and manned the wings with a force of infantry,” keeping up a murderous suppressive fire so that the attacking troops could not “raise even a hand above the crest without having it pierced by a dozen bullets.” Worse, the explosion had also pulverized the loess soil into a fine sand that, once it had settled in the crater, defied efforts to climb out of it.
As the defenders rained grenades down on the Federals in the approach sap, Hickenlooper moved his prepared overhead protection into place. There was little he could do to affect the outcome anymore. In retrospect, he might have done better to construct ladders, and such thoughts probably agonized him later.
At one point during the desperate action, Lt. Stewart R. Tresilian, an Irish engineer, saw that Confederates inside the redan were gathering for a charge. Tresilian “dashed to a nearby Federal battery and obtained ten-pound Parrott shells that he rigged with “five-second fuses” and threw over at the enemy,” Woodworth and Grear write. “Tresilian hurled his bombs one after the other, a feat that stopped the Confederate advance in its tracks.” Nevertheless, “the close proximity of the fighting and the bunching up of Union troops in the confined killing space of the crater led to horrific casualties.”
Altogether, 34 Union soldiers were killed and over 200 wounded. “Nothing … was gained by blowing up the fort, except planting the stars and stripes thereon,” Osborn Hamiline Oldroyd, a soldier of the 20th Ohio, wrote days later.
Sauna-like seasonal conditions, lost sleep, tireless work, and “nervous strain” led Hickenlooper to “nervous prostration,” as he called it, in the days after the failed assault. Confined to his tent for four days, he was in a state of “total collapse,” “incapable of physical exertion.” Apparently at death’s door, he received a personal visit from Grant, and after a sardonic exchange, began to recover the next day. Today, we would probably use the language of therapy to describe Hickenlooper’s ailment as acute depression. Soldiers would perhaps call it survivor’s guilt. He had given everything, accomplished more than he had ever achieved in his life, and still failed.
Lt. Tresilian, on the other hand, was still at work. Prime and Comstock report that “the enemy’s salient here being too high for our men to be able to return the grenades which they threw upon us so freely, and having no Cohorn mortars,” the Irish civil engineer “had some wooden mortars made by shrinking iron bands on cylinders of tough wood, and boring them out for 6 or 12 pound shells.” Surprisingly, “these mortars stood firing well, and gave sufficiently good results at 100 or 150 yards distance.”
Vicksburg surrendered on 4 July 1643. Grant had cut the Confederacy in two, depriving the rebel war machine of its riverine economy. On the previous day, defeat at Gettysburg had forced Robert E. Lee to withdraw from Pennsylvania, never to attack the north again. Defeat was now a certainty for the Confederate States of America, resist as bloodily as they might. And they would resist with blood.
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