8,800 days’ worth of work: Constructing the Marsh Battery

Time for me to catch up on the story of the Swamp Angel of the Marsh Battery.  At the end of last month, I wrote about the reconnaissance by Colonel Edward Serrell into the marshes behind Morris Island.  He and his engineers probed and examined the mud in an effort to solve the problem which Brigadier-General Quincy Gillmore had given them – how to build a battery supporting one of the heavy Parrott rifles in the marsh.

During the first days of August, Serrell’s team conducted some experiments to determine the behavior and load bearing capacity of the marsh mud.  After building a platform on the mud flats, the team piled on sandbags to reach a loading of 400 pounds per square foot.  That stood for a day without settling.  So they added more weight to reach 650 pounds per square foot. Other than leaning to one side, the platform sustained the weight.


The engineers continued piling on sandbags, pushing the experiment as only engineers will do.  Serrell recorded these results:

After about another hour and a half, additional bags were piled upon the column, until a force of about 900 pounds to the square foot on the platform had been obtained, when the whole suddenly upset, throwing sand-bags all over… the platform, however, sank but about a foot at one corner, and the trial was considered merely as showing that the sustaining strength of the marsh was equivalent to over 600 pounds to the square foot, where the load is uniformly distributed.  The ultimate sustaining strength was not ascertained.

The figure above shows a “ghost” of the test structure after it tipped over.

But Serrell was not simply setting up a 16,500 pound gun and its carriage on a platform in the marsh.  He had to set it up for use.  The recoil forces might push the gun and platform around the marsh.  Or the vibrations caused by firing might damage the platform.  And worse yet, if a platform that could sustain the gun on the marsh was designed, exactly how would the engineers build it under the eyes of the Confederates on James Island?

The final design was one of classic improvisation in the face of adversity.  First, the engineers would put down a set of pilings to form a box within the mud.  At first the work crews, detailed from the 7th New Hampshire Infantry, drove the pilings with a long lever anchored to a counter-weight.


But the crew found difficulty moving the counter-weight:

 Instead of a counter-weight, a number of men took hold of the pole at either end, and having the plank secured by a sling, it was forced down into the mud until the point reached the hard bottom, when it was driven into the sand securely by heavy wooden mauls.


So with these pilings forming an open topped box in the march, a platform for the gun was built within.  The platform consisted of a layer of grass, two layers of tarpaulin, 15 inches of sand, then three layers of 3-inch thick white pine planks.  Only the top layer of the gun’s platform touched the pilings, and even at that only to cover the sump between the pilings and the platform.  The pilings were not load bearing in that regard.

The engineers then built a parapet around three sides of the platform.  They started with a layer of dried swamp grass, on top of which they placed two layers of heavy canvas.  Then on top of that the crew laid two layers of yellow pine logs to form a “grillage.”


The layers crossed at right angles and were fixed with bolts and wire.  The crew filled the gaps between the logs with sand and broken sand-bags.  As with the gun platform, the parapet’s grillage did not rest upon the pilings.  Upon the grillage, the crew piled sandbags… lots of sandbags.  Most of the 13,000 bags used in the construction went into the parapet.

The result was a structure detailed in Serrell’s drawings:


So how did this keep the massive gun from sinking? Well as Serrell described:

 The foundation of the parapet receives a much greater load to the square foot than the gun-deck, and the resultants of the forces are tending rather to elevate the whole structure on which the gun rests than to allow it to settle.

That is, if the battery should sink in the mud, the gun would be left standing on its own foundation, while the displacement would elevate the surface of the surrounding marsh, and tend, so far as it acted through or under the sheet piling which surrounds the gun platform, to elevate it also.

An illustration might help the translation from “engineer-speak.”  The box formed by the piling confined a column of marsh mud.  That column received pressure, thus keeping the gun platform elevated even with the weight of the gun, as the parapet pressed down on the grillage.  Following the colors, the red arrows depict the pressure down from the parapet weight.  The yellow arrows show how the pressure was dispersed.  The green arrow is the pressure confined within the pilings, pushing the gun platform up:


Feel free to comment about fluid dynamics or other brainy topics.  The bottom line is this work was a set of moving parts.  The pilings also served to dampen the recoil force.


In addition to the 13,000 sand bags, Serrell recorded:

… 123 pieces, 15 to 18 inch diameter yellow pine timber, 45 to 55 feet long; 5,000 feet 1-inch boards; 8 [tarpaulins], 18 by 28 feet each; 9,156 feet 3-inch pine plank; 300 pounds 7-inch, and 300 pounds 4-inch, spikes and nails; 600 pounds round and square iron; 75 fathoms 3-inch rope.

All those materials were in addition to the gun, carriage, and ammunition. To move these materials, work crews built a road connecting the battery to the landing on St. Vincent’s Creek.  In addition, a plank walk way extended from the left breaching batteries, across the marsh to Black Island and the Marsh Battery.



The walkway included a platform for a guard force, should the Confederates attempt to disrupt the construction.  Other security measures included guard boats with howitzers and booms across the creek.

Serrell offered these particulars of the work on the Marsh Battery:

  • Average pressure on the foundation – 513 pounds per square foot.
  • Average pressure on the gun-deck platform – 123 pounds per square foot.
  • Elevation of the gun from 35° to 37°.
  • Greatest range to Charleston – 9,240 yards, or 5 ¼ mile.
  • Labor expended – 91 man/days of engineer officer labor, 1,384 man/days of engineer soldiers, 7,390 man/days detailed infantry, 172 days’ work of four-horse teams, and 93 days’ work of boats.

On the night of August 17, Lieutenant Andrew Wadlie, 3rd New Hampshire Infantry and Lieutenant Charles Parsons, 1st New York Engineers, supervised the placement of an 8-inch Parrott rifle in the Marsh Battery.  The gun they moved was this one:

Trenton 14 Aug 10 382

Do we have pictures of this big Parrott in the battery?

We’ll get to those shortly!

(Citations from OR, Series I, Volume 28, Part I, Serial 46, pages 232-235.)

150 years ago: Fourth parallel at 350 yards from Battery Wagner

August was a busy month on Morris Island, 150 years ago. And the busiest days occurred from August 17 through 23 with the simultaneous bombardment of Fort Sumter, advance of the siege lines against Battery Wagner, and the little matter of a Parrott Gun firing on Charleston. Add in Confederate attempt to sink the USS New Ironsides and the week’s worth of activity becomes one of the most interesting of the war. Not to be outdone by the actions of man, a gale blew in from the Atlantic Ocean on August 18 and continued through the 21st. What we would refer to as a “storm surge” in combination with a spring tide filled the trenches of the parallels and boyaux with water. The storm also took out the surf battery’s parapet, and forced the temporary removal of the howitzers. The aim of the heavy Parrott guns was not significantly affected by the storm’s winds, so the big guns continued their work. However the same could not be said for the work advancing the siege lines towards Battery Wagner.

After the construction of the third parallel earlier in August, Brigadier-General Quincy Gillmore suspended the advance of more parallels pending the bombardment of Fort Sumter. On the night of August 18, Gillmore ordered the engineers to resume the advance, despite the weather. Major Thomas Brooks recorded minimal work was completed that night:

… the trench of this parallel was cleared out and widened, the parapet strengthened, and the debouch made. A Requa battery was placed in position on the extreme left of the third parallel, to enfilade the front of the parapet of the proposed sap. Sap-rollers and sapping tools were carried forward. The extreme high tide, requiring the men to work in mud and water, greatly interfered with all these operations.

The immediate objective of the next parallel was to reach past a set of fingers extending from the marshes, which neared the beach at several points. This was the narrowest section of Morris Island, and which had proved so difficult to traverse in the July assaults on Battery Wagner. Accordingly the engineers approached with careful deliberation and caution. Adding to the difficulty were the presence of Confederate sharpshooters on a sand ridge in front of Battery Wagner. Referencing the map below, provided by Colonel Edward Serrell in his report, the sand ridge is to the right (however, disregard the location of the fourth parallel for the moment).


The plan was to run the sap out from the third parallel past those marsh fingers. Then construct a parallel running from the beach across to the marshes. Such would put the next parallel within 200 yards of Battery Wagner. The work resumed in the early morning hours of August 19:

This morning at 2 o’clock, the water having so subsided as to render it possible, the full sap was started from the point above indicated, by Captain [Joseph] Walker, with a sapping brigade, consisting of 10 men from his own company (I, New York Volunteer Engineers). He had executed 60 feet at 8 a.m., and was then relieved by Captain [John L.] Suess, with a sapping brigade from his company (B), same regiment, who completed 70 feet of approach during the day. The enemy’s sharpshooters opened on the head of the sap as soon as they observed its progress in the morning, and fired at it all day. One casualty occurred among the sappers, a slight wound from the explosion of a shell. Captain Walker again took the advance this night, and, by means of the flying sap, executed about 160 yards of approach, leaving the sap-roller at daybreak in position several yards in advance of our picket line.

The advance here being measured in yards, with the Federals then about 200 yards closer to Battery Wagner, but without a parallel. As indicated by Brooks, the sapping details worked in shifts, and cycled through rest periods similar to those of the men in the breaching batteries. With that work ever so close to Confederate lines, Brooks made arrangements for an advanced guard, consisting of a full regiment of infantry, positioned in the forward trenches of the third parallel (and recall the “keeps” of that trench line).

On the morning of August 20, a detail under Lieutenant Charles Wilcken took over the work on the sap. The work proceeded slowly during the day. Three of the detail were injured. By mid day, Captain Suess’ detachment took up the work. Finally around six that evening, Lieutenant Charles Parsons brought a fresh detail into the trenches. Six hour shifts during daylight hours, with longer runs at night.

Captain Walker’s detail returned to the sap at 3:30 am on August 21,

… at which time the enemy were directing a heavy fire of grape and canister upon it, which fire ceased before daylight. This permitted him to place a line of gabions on the reverse side of the trench, to shield the sappers from the enemy’s sharpshooters, who, it was feared, would occupy the cover furnished by the old ruins to the front and head of the sap.

At that point, the engineers could not move farther forward. Artillery fire from Battery Wagner and sharpshooters on the ridge kept the sappers pinned down. When Wilcken’s crew took over duties, he was forced to retire. A flag of truce went out at 11:30, but by noon hostilities resumed.

In response to this resistance, the Navy brought up the USS New Ironsides and several gunboats to fire on Battery Wagner. Likewise the 30-pdr Parrotts and field guns in the Federal batteries fired in support of the sappers. General Alfred Terry ordered up the 100th New York Infantry, under Colonel George B. Dandy, from the keeps of the third parallel to conduct an evening assault on the Confederates on the ridge. Despite several attempts and the loss of six men, the New Yorkers could not gain the ridge.

Brooks considered the situation that night and determined to at least secure what was gained:

I examined the ground, and concluded to establish a fourth parallel, in order to secure possession of the ruins on the elevated ground to the left, from which the enemy’s sharpshooters had long given us so much annoyance, and to increase our front preparatory to another attempt to take the ridge. This parallel, comprising a linear development of 300 yards, was opened from the beach to the marsh, close along the heels of our outposts (its right being 350 yards from Wagner), by Captain Suess. He reports most part of the work was done by means of the flying sap, the engineers placing the gabions and the negro troops (Third Regiment United States Colored) digging the trench. The part on the left, near the ruins, being constantly swept by the enemy’s musketry fire, was performed by the full sap; not, however, using the sap-roller, as a flank fire only had to be provided against. The details for this advanced work this night were 100 infantry and 15 engineers.

The resulting trench lines appear on Brooks map of the approaches to Battery Wagner (here with the third and fifth parallels for context):


I’ll save the discussion of the Requa and coehorns for later. But notice the fourth parallel fit between two of the marsh fingers. At first glance, this might seem a bad position. But the extent of 300 yards of trenches allowed more room to maneuver for the Federals.

Brooks offered two profiles of the trenches on the fourth parallel. The line m-m’ was across the approach boyaux just behind the parallel. Here the engineers used a barrel to help form a step up to the banquette.


Profile n-n’ was along the actual parallel trench. Here the engineers used gabions to raise the height of the works and allow the infantry to better defend the line.


Notice that in both profiles the trench’s ditch was wide enough to accommodate more troops, equipment, and weapons.

I’ve run a bit long in the description of the fourth parallel. But much of that was a “setup” of sorts. The take away here was how the action at the point of advance evolved into something which had similarities to … say… actions in the Central Pacific during World War II. An assault force worked foot by foot against an entrenched enemy, supported by heavy artillery and naval gunfire. Covering fire from the Billinghurst-Requa “machine-guns.” No fancy maneuvers to consider. Close quarters night actions. Spade, musket, and bayonet. And the fighting along the fourth parallel was just starting as August 22 dawned. The Confederates could not let this advance could not go uncontested.

(Citations from OR, Series I, Volume 28, Part I, Serial 46, pages 288-290.)