Lou's Place in Cyberspace
The gun that fired on Charleston,
by Lou Robertella.
In the early morning of July 10, 1863, Major-General Quincy A. Gillmore of the l0th Army Corps moved his command before the defenses of Charleston, South Carolina. Charleston was one of the two major Confederate ports through which munitions and other war supplies from Europe had to pass. The U. S. Navy had blockaded the Southern seaports along the Atlantic seaboard but its efforts to blockade Charleston harbor was not being totally effective. Every day Confederate blockade runners were slipping into port, taking advantage of the complicated currents and shifting shoals of the harbor entrance. Capturing Charleston was the only way to cut off this important supply line. Charleston had been the seat of the Rebellion, and the scene of the opening engagement of the Civil War when Fort Sumpter was first attacked on April 12, 1861.
At the entrance to the bay are several islands that were sites for Confederate shore batteries and forts that could fire on U. S. Navy ships trying to enter. On the left of the bay, or south of the entrance, are James, Morris, and Folly islands. On the right, north of the bay entrance, is Sullivan's Island. These islands are mostly large sand reefs. In the center of these two island groups, and in the center of the harbor entrance, was the former U. S. Garrison, Fort Sumpter, which remained under Confederate control. (MAP 1)
Extending up the harbor on either side, lay other small islands and reefs, with marshes stretching between them, and many winding, narrow creeks.
Just before sunrise on July 10, forty-seven mortars, siege, and field guns, located on Union held Folly Island, and four ironclad monitors, opened fire on the Morris Island defenses. After a two-hour bombardment, the order to assault the island was issued, and storming parties began landing on the beachhead.
By 9:00 A.M., three-fourth's of Morris Island and all the Confederate batteries on the south end of the island, had been captured, along with eleven pieces of Confederate artillery. Union forces were then within rifle range of Fort Wagner, the most formidable Confederate installation located on the northeasterly end of the island. Fort Wagner was well defended and fortified.
Beyond Fort Wagner was Battery Gregg on Cummings point, the northeastern tip of Morris Island and nearest to Fort Sumpter. (MAP 2)
Union batteries were established in several locations on Morris Island and these batteries began to fire on the Confederate positions, including Fort Sumpter. These Confederate positions, especially Fort Wagner, which stretched completely across the narrow northern end of the island, were making it almost impossible for the Union forces to advance closer to the city. (MAP 3)
Battery Kirby, a Union battery located on Morris Island, was the only Union battery able to throw shells some 4,550 yards into Fort Sumpter. Their shells were only able to reach the fort it they had a favorable tailwind and they used an additional two pounds of powder over the regular charge. Otherwise their shells would fall short, and they would then cease firing until the wind changed again in their favor. It was during these bombardments by the Union artillery that the idea of firing directly on the city of Charleston was conceived by General Gillmore. General Gillmore believed that if the city itself were threatened with destruction, the Confederate authorities would be forced to surrender the city and the defenses protecting it. Gillmore believed it might be possible to mount a large gun in the swamp, closer to the city, and reach the city with artillery fire.
On the morning of July 13,1863, General Gillmore directed Lieutenant Peter S. Michie, United States Corps of Engineers, to make an examination of the marshes before Charleston and determine if it were possible to construct a battery that would be capable, from its advanced position, of throwing shell into Charleston. After considering the idea, Michie reported that it would be possible to build such a battery.
While at breakfast on July 16, General Gillmore told Colonel, Edward Serrell, Volunteer Engineers, (later to become a distinguished civil engineer of the City of New York), of his idea and instructed him to investigate the feasibility of constructing a battery on the marsh surface.
After breakfast, Colonel Serrell accompanied by Lieutenant Nathan M. Edwards of his own command and carrying a 14 foot plank between them, started across the swamp to begin making tests of the weight bearing capacity of the marsh surface. They had to determine what uniformly distributed weight the surface could bear.
They walked out onto the mud as far as possible before they began to sink into the surface muck. It was estimated that a man weighing 150 pounds would sink some 18 inches into the marsh at each step. The bottom of the marsh was sand and the surface covered with dense reeds and wild grass some four feet high. To move across the marsh surface, Serrell and Edwards would lay the plank on the surface, walk out to the end, straddle it and quickly push it ahead of them, repeating this process until they found a suitable test site. The day was intensely hot, and they were in open view of four Confederate forts and eleven batteries.
Colonel Serrell selected a site "at a point bearing from the southwesterly end of hard ground [on Morris Island-LAR] a course by magnetic compass north 40 degrees west to a point from which the bearing to Fort Sumpter is north 12 degrees east and to the old beacon light south 86 degrees east." (About 7900 yards or 4.49 miles from Charleston-LAR)
After selecting a site, tests were conducted using a four foot square platform made of 3-inch plank, which was laid upon the surface of the mud. The platform was then loaded with filled sandbags, piled carefully in regular layers, until a load of four hundred pounds per square foot was attained.
Although the mud was so soft the sandbags could not be carted to the test site, except by walking on boards, the column of sandbags on the test platform remained erect. After standing for twenty-four hours, the platform showed no signs of settlement. The mud was twelve feet deep under the test platform.
After the test platform had stood for twenty-four hours, additional sand bags were piled upon the column, and when it reached a height of about seven feet, corresponding to a pressure of about six hundred and fifty pounds per square foot, the column began to lean towards the approach used by the soldiers to load the sand bags. After another hour and a half, additional bags were piled upon the columns until a force of about nine hundred pounds per square foot was on the platform.
Suddenly the platform sunk down in one corner, throwing the sand bags over, and burying many of the upper tiers, which fell the farthest, out of sight in the mud. The platform, however, only sank about a foot at one comer, and like a punch, cut its way cleanly into the surface. These tests showed that the sustaining strength of the marsh was equivalent to over six hundred pounds per square foot. The ultimate sustaining strength of the surface was never determined, but they had enough preliminary data to begin the calculations necessary for the construction of the battery.
On July 30, many soundings were made at various points using a 30 foot, 3/4 inch iron rod as a probe. The mud was found to average about 20-feet deep in many places. During most of the probes, the rod would sink of its own weight, almost ten feet down, and then could easily be pushed to the bottom by hand.
It was noted: "Some idea of the Jelly-like consistency of the mud may be conveyed by stating that two men standing upon a plank could, by the proper motions, make the entire mass beneath them visibly move for several hundred square yards."
On the morning of August 2, a general plan for the battery was submitted by Colonel Serrell to General Gillmore, who after reviewing the engineering data approved it, and ordered an estimate of the labor and time necessary to build it.
That night, the estimate was calculated. The engineering staff concluded that about ten thousand day's work was required for its construction. General Gillmore gave his final approval and the battery ordered constructed.
The engineering details of the battery were left in the hands of Colonel Serrell. His design called for the construction of two separate platforms. One platform, the larger of the two, would hold the parapet and epaulement, The other smaller platform would hold the gun and gun carriage only. The design was such that the gun platform would remain relatively stationary while the parapet section would float independently on the marsh surface.
The large platform holding the parapet, would act as a hydraulic ram, it's weight and pressure on the surface would help keep the gun deck stable, even if the parapet section should begin to slowly sink.
Colonel E. W. Serrell described his construction scheme as such:
"The gun-platform was placed upon a gun-deck resting upon vertical sheet piling, outside and around which there was a grillage of logs. If the gun and the other weights upon the gun-deck were heavy enough to tend to sink in the mud, the weight upon the grillage, in the form of sandbags, which formed the parapet and epaulement of the battery, by being increased counterpoised the gun-deck. It was simply a force meeting another force of a like amount in an opposite direction."
First, a detail of several hundred men began cutting down trees on Folly Island. After the trees were cut, they were floated over to the proposed battery site. On Morris Island, men were detailed to fill sandbags and to hide them so as the enemy would not suspect anything, then move them by night to a staging area. Other soldiers were directed to cut down and trample the swamp reeds and rush's into the surface mud at the selected site, creating a matted mud stratum that was quite firm.
Two layers of 18 X 28 foot canvas tarpaulins were laid down completely covering the treated area. Over the tarps, large pine logs 40 to 55 feet long, 15 to 18 inches in diameter, were laid out in rows, side by side, in two groups of about 20 logs each. The reeds that had been trampled into the mud before this, were trampled transversely to the direction of the logs that were placed on the tarps.
These two groups were laid parallel to each other with an open 20 foot space between them. The logs in each group were then bolted together. (Fig. 1 and 2)
Next, over these logs were laid two more groups of logs running perpendicular, or at right angles, to the first mentioned logs. These additional two groups were also parallel with each other and having a 20foot space left between them. This arrangement formed a hollow square in the center of a large square log platform. In the outer corners where the logs overlapped, the logs were two layers deep. (Fig. 1)
The 20 foot square area between the logs, the hollow square, where the trampled gross and mud still remained, was to be the position of the gun platform. (Fig. 3)
After the logs were bolted together, sand was poured between them, along with remnants of sandbags broken in transportation. Around the perimeter of the log platform additional damaged sandbags were piled forming a kind of ramp to give additional weight near the surface of the surrounding marsh, to help keep it from rising unequally if the battery should sink.
Around the inside edge of the hollow square, in the center of the larger platform, sheet piling, which were large 12 inch by 3-inch by 40 foot planks having one end cut on a bevel, were driven down into the mud, forming a vertical interior box extending down to the marsh substratum. The bevel on the leading edge of the piling would help force each piling up against the piling next to it.
This interior box, formed from the sheet piling, was to be the only part of the structure firmly mounted to the floor of the swamp. The large parapet platform of crossed logs described above, called a "grillage," was basically a large platform floating on the mud surface. The smaller interior box, formed by the sheet piling for the gun platform, was essentially anchoring and holding the outer platform from drifting or moving laterally. (Figs. 4 & 7)