In the evening of August 9, 1863, Brigadier-General Quincy Gillmore passed the word down to his subordinate leaders on Morris Island to open the third parallel against Battery Wagner. The operation, which the engineers and infantry had prepared for over the previous week, entailed the construction of a boyaux from the second parallel and then construction of another main trench line. When dawn came on August 10, the Federal lines were only 540 yards from Battery Wagner.
Well that was the short description of what happened, of course not counting the great difficulty of such operations. Major Thomas Brooks explained in his journal:
The engineering difficulties anticipated at this time in the construction of the approaches against Wagner were–
First. The narrow front on which to conduct the operations, together with the scarcity of earth for covering masses, as heretofore experienced.
Second. The heavy cross-fire from Wagner and Sumter, Battery Gregg, and the James Island batteries, which will necessarily take in reverse and enfilade a part of our trenches; together with the vigilance, skill, and obstinacy of the enemy’s sharpshooters.
Third. The difficulty of protecting the flanks of our parallels from being turned by the sorties of the enemy. At each low tide our right flank, as we progress, will be irreparably open. At all times the dry, intermediate marsh, between mud and sand, on the left endangers that flank, for this marsh is too wet to trench, but still entirely passable for troops.
There was no real solution for the first two issues. The terrain worked against the Federals for this siege line approach just as it did on July 18 for the infantry assault. But for the third, Brooks and the engineers came up with a couple of plans. One called for extensive abatis and palisading along the lines of advance. This was rejected due to lack of materials. The second, less expensive on material, involved construction of keeps for positioning of the advance guard as the trenches moved forward. That of course meant the infantry must post a substantial force in the trenches, day and night, in order to quickly meet any Confederate attacking force. This second option was approved.
The previous day Brooks had his engineers conducting experiments to determine the best techniques for advancing the lines:
Fired 30-pounder Parrott rifle projectiles into a sap-roller; ascertained “constraints of work” (work of one man for one hour) in a trench; also penetration of rifle-balls into wet and dry sand, facines, pine planks, and palmetto logs.
These experiments helped set the techniques used when the time came to construct the next parallel. Additionally, on the night of August 8, Brooks and other engineers went forward to inspect the ground on which the third parallel would be constructed.
As mentioned above, the word to advance the lines came on August 9. Brooks provided, as was his style, a detailed account of the work:
The detail for to-night’s work is 124 volunteer engineers, under Lieutenants [Hiram] Farrand and [Edward] Talcott, and 80 infantry, under Captain [Joseph] Walker. The engineers were in advance. Two hundred and sixty yards of trench were opened, and a splinter-proof parapet, from 6 ½ to 8 feet high, built throughout its length. No portion was revetted. Our grand-guard outposts were but 30 yards in front of the working party, and the enemy’s pickets, who could be seen, were apparently not over 30 yards farther. The engineers, on their knees, shoveled almost noiselessly. I could scarcely hear or see them from the line of outposts, 30 yards distant. The following method of setting the engineers at work was adopted: They carried no arms. Each man held a short-handled shovel in his right hand; in the left, at intervals of 6 feet, each grasped a marked rope. The engineer officer who located the line took the lead. The men marched forward, stooping. At a signal the rope was dropped, and each man went to digging a pit where he stood, throwing the earth over the rope. These pits were connected, and good cover was soon obtained.
And let me draw a fine point here – Brooks never mentions the use of a sap-roller during that night. The results were the basic system of trenches seen on Brooks’ map of the siege lines:
On the left is the right end of the wire entanglements and advanced positions on the second parallel. The work on the night of August 9-10 had to first run a boyaux through that line and out to the narrow formed between the mash and the beach. Before moving to the work on the third parallel, let me point out the profile of those defensive works advanced from the second parallel. Brooks provided a profile of those works, marked by the line h-h’ on the map above:
The palisades and wire on the right are part of the main defensive line. Notice however the splinter-proof and parapet on the left are not perfected to allow firing to the front. Those works were constructed to protect a force of men being held in reserve, without exposing them to fires – both friendly and enemy. The strength of this line lay in the obstacles and the howitzers to the immediate rear.
Further to the right of the map crop above is the first of three profiles Brooks provided for the third parallel. This one is a three point profile from g-g’-g”.
Anchoring the right end of the third parallel was a mortar position. These mortars went into the line on, or about, August 23. Forward of that position was another splinter-proof for the soldiers detailed for guard duty. But look back towards the left at the profile of the main parapet. The profile demonstrates the firing steps and other arrangements made so the infantry could defend this line with muskets.
Looking to the middle of the third parallel, another profile was drawn on the line i-i’:
We see here, in the center of the profile, the “keep” described by Brooks. Again there is a firing step for the infantry who have to defend this line. The abatis to the front was not as elaborate as the wire entanglements on the second parallel. To the rear was a line of vertical palisading. But again, not as elaborate as the main defensive line. That palisading attracted unwanted attention from the Confederates in the early morning hours of August 11:
At about 2 o’clock on the morning of the 11th, when the last-mentioned work was about one-half completed, Wagner opened a heavy fire of grape, canister, and shell, which, with the fire of the James Island batteries and Sumter, stopped our working parties entirely for the first time in the siege. Lieutenant Farrand, who had charge of the work, supposed that the tall palisading which was set across the gorge of the keep attracted the fire. This is the most spiteful fire delivered landward by Wagner since the 18th July. Indeed, this work has been very quiet since that time for fear of drawing the fire of the heavy guns of the navy, and that of the land siege batteries upon it. Our reply to all the enemy’s fire, from whatever direction, has been directed against Wagner.
Looking further along the third parallel, another profile runs the line k-k’:
This profile runs across a position for a Billinghurst-Requa gun anchoring the left flank of the parallel. The step formed by a “powder-barrel revetment” mimics the steps of the infantry line.
After the advance of the third parallel, the engineers would focus their efforts at improving the battery positions as the countdown to the big bombardment ticked. The overall plan, recall, was to use those big guns to do the work. As Brooks related, “these approaches would probably only amount to a feint, as, on the demolition of Sumter, the monitors can invest Morris Island, and thus reduced Wagner and Battery Gregg.” But things wouldn’t work out exactly like that.
(Citations from OR, Series I, Volume 28, Part I, Serial 46, pages 282-4.)