What was the most significant event on June 16 during the U.S. Civil War?

Early morning assault bogs down in marshy and muddy area in 1862: Federal forces assault failed on the confederate defenses around Charleston, SC on James Island.
1863: CSA Gen Robert E. Lee is moving the infantry and artillery of the Army of Northern Virginia while the cavalry is screening and foraging and moving ahead in Pennsylvania. Most likely he had no idea of the carnage that awaited his Army in the vicinity of Chambersburg at a place known as Gettysburg.
1863: Confederate Cavalry General Albert Jenkins was “of good stock.”
“The Confederates were a mostly well behaved lot. They hardly bothered the farmers, did not tear down fences, and took only a few of the cattle. Most things they took were paid for in Confederate script. Jenkins and his men cleaned out the downtown merchants, who were hardly amused with being paid in such worthless notes.”
“General Jenkins and his Confederates paid for everything, but three particular items:
(1) “horses, which he considered contraband of war. When the horses were found to be in short supply;”
(2) weapons in the town. “Any make or model would do. When delivered, he destroyed the worthless and kept the finest.”
(3) “black people. His men rounded them up like they had wanted to round up horses. Slave, free, man, women, or child, it did not matter. To them, a black person was a slave and nothing more.”
Tuesday June 16, 1863: Corporal James Kendall Hosmer, a Union soldier with Gen. Banks’ Army of the Gulf besieging Port Hudson, writes of the miseries of serving in the infantry investing a besieged fortress, and of the graphic experience of making an assault: “ The Fifty-second Regiment are holding an advanced position here, and, ever since daylight of the morning of the 14th, have lived in the midst of a rain of rifle-balls. At the bottom of the little ravine, I am secure; but if I should put my head up to the surface, climbing up the bank six or eight feet, I should be in the midst of flying bullets, and a fair mark for the rebel sharpshooters who are close at hand. Our brigade is thrown out into the very teeth of the enemy, on ground our troops have never before occupied. This little corner is occupied by the color-guard. If I go to the company, I must go stooping or crawling on my stomach; I must run from a stump to a trunk, and from that to a clump of bushes, and hear all the time the “zip” and “hum” of the rifle-balls. . . .
The work of death had begun; for ambulance-men were bringing back the wounded: and, almost before we had time to think we were in danger, I saw one of our men fall back into the arms of his comrades, shot dead through the chest. The banks of the ravine rose on either side of the road in which we had halted: but just here the trench made a turn; and in front, at the distance of five or six hundred yards, we could plainly see the rebel rampart, red in the morning-light as with blood, and shrouded in white vapor along the edge as the sharpshooters behind kept up an incessant discharge. I believe I felt no sensation of fear, nor do I think those about me did. Wilson and Hardiker carried the flags, and their faces were cheerful and animated. . . . .
In a minute or two, the column has ascended, and is deploying in a long line, under the colonel’s eye, on the open ground. The rebel engineers are most skilful fellows. Between us and the brown earth-heap which we are to try to gain to-day, the space is not wide; but it is cut up in every direction with ravines and gullies. These were covered, until the parapet was raised, with a heavy growth of timber; but now it has all been cut down, so that in every direction the fallen tops of large trees interlace, trunks block up every passage, and brambles are growing over the whole. It is out of the question to advance here in line of battle; it seems almost out of the question to advance in any order: but the word is given, “Forward!” and on we go. Know that this whole space is swept by a constant patter of balls: it is really a “leaden rain.” We go crawling and stooping: but now and then before us rises in plain view the line of earth-works, smoky and sulphurous with volleys; while all about us fall the balls, now sending a lot of little splinters from a stump, now knocking the dead wood out of the old tree-trunk that is sheltering me, now driving up a cloud of dust from a little knoll, or cutting off the head of a weed just under the hand as with an invisible knife. I see one of our best captains carried off the field, mortally wounded, shot through both lungs, — straight, bright-eyed, though so sadly hurt, supported by two of his men; and now almost at my side, in the color-company, one soldier is struck in the hand, and another in the leg. . . . Presently we move on again, through brambles and under charred trunks, tearing our way . . . creeping on our bellies across exposed ridges, where bullets hum and sing like stinging bees; and, right in plain view, the ridge of earth, its brow white with incessant volleys. . . . Down into our little nook now come tumbling a crowd of disorganized, panting men. They are part of a New-York regiment, who, on the crest just over us, have been meeting with very severe loss. . . . From time to time, afterwards, wounded men crawl back from their position a few yards in front of where we are, — one shot through the ankles, who, however, can crawl on his hands and knees; one in the hand; one with his blouse all torn about his breast, where a ball has struck him, yet he can creep away. . . .
It is now noon and after. The sun is intolerably hot, and we have no sufficient shade. That, however, is nothing for us who are unhurt; but we hear of poor wounded men lying without shelter, among them Gen. Paine, whom the ambulance-men cannot yet reach on account of the enemy’s fire. We begin to know that the attack has failed. . . . We have not been as much exposed as some other regiments, and our loss has not been large. The fire, however, seemed very hot, and close at hand; and the wonder to us all is, that no more fell. Darkness settles down; shots are received and returned, but only at random now; and, ever and anon, from the batteries goes tearing through the air a monstrous shell, with a roar like a rushing railroad-train, then an explosion putting every thing for the moment in light. . . . For food to-day, I have had two or three hard crackers and cold potatoes. We have no blankets: so down I lie to sleep as I can on the earth, without covering; and, before morning, am chilled through with the dew and coldness of the air. . . .”
[At night] I climbed up from the ravine, and sat alone, upon the hill on the field, under the starlight. It was a sweet night, and only once or twice came to my sense the taint of unburied slain. For the rest, all was pure. In a half-comic way, the whippoorwill changed his song into “Whipped you well, whipped you well!” I will never believe the bull-frogs that night croaked any thing but “Rebs, rebs!” and the jeering owls hooted out from the tree-tops, “What can you do-o-o?” All about the horizon, fringing the starlit space of blue, a storm was gathering; and behind the black clouds shook the lightning, like the menacing finger of an almighty power threatening doom to this obstinate stronghold. . . .”

Pictures: 1862-06-16 Secessionville SC battle map; 1864-06-16 The charge of the 22nd Negro Regiment, Petersburg, Virginia; 1864-06-15 Petersburg June 15-16; CSA Gen Stonewall Jackson
A. 1862: Battle of Secessionville, South Carolina. Brigadier General H. W. Benham attacks forces under CSA Brigadier General Nathan "Shanks" Evans near Charleston. The Federal army came close to capturing a vital position on James Island, but Federal General Benham's poor planning and the timely arrival of reinforcements resulted in a victory for the outnumbered Confederates.
The Confederate advanced pickets were overrun about 5:00am, this activity alerted the defenders. Col. Lamar mounted the parapet to observe the Union front about 700 yards and closing. He immediately dispatched couriers to Gen. Evans, who was five miles away at Fort Johnson with the reserves. As the defenders rushed to their stations, Col. Lamar took personal command of the 8-inch-Columbiad. The Union lines were within two hundred yards of the fort, Lamar order the Columbiad to fire; grapeshot, nails, iron chain and glass blasted from the cannon directly at the Union center, tearing a great hole through the Federal lines. The Battle of Secessionville had commenced.
Col. Lamar sharply ordered all gun commanders into action and moved the infantry into place firing volleys as they came onto line. The 8th Mich. on the Union right, was now clambering up the face of the fort followed by the 7th Conn. troops and soon after the 28th Mass. The arrival of Confederate reinforcements drove the Federal assault force back from the parapet when the Confederate defense was on the verge of collapse due to casualties on the critical gun crews. The Federals came under severe fire from three sides as they advanced up the fort walls, only to be ordered to fall back to regroup after suffering heavy casualties. Meanwhile the 79th NY on the Union left actually mounted the fort's parapet and were engaged in hand-to-hand combat with the Rebs, when the Union artillery, located at the River's house, opened fire on that fort breaking up the Union attack and forcing the 79th to withdraw. As the first Federal wave collapsed and retreated they hampered the second wave from attacking.
The Federals fell back to the protection of the hedge rows to reformed their lines. They were to make two more unsuccessful assaults before a general withdraw was ordered. While the main assault was taking place the 3rd New Hampshire was attempting a flanking maneuver from the federal left. Their assault brought them to within several yards of the flank of the fort, but they could not make a full assault due to the water and pluff mud that proved to be impassable. They proceeded to assault the fort from across the marsh driving the defenders from the parapets. The two 24-pounders Lamar set up on his right flank were still silent, even though the new gun crews were on line. Lt. Col. Ellison Capers of the 24th SC infantry was sent up to the position to determine the problem. The gun crew, although an artillery unit, had never been trained in firing a cannon before and did not know what to do. Capers sprang into action loading and firing the piece himself, while training the gun crew. Meanwhile 250 men of the 4th LA Battalion arrived from their encampment 2-1/2 miles away to sure up the confederate flank and pour a decimating fire into the 3rd NH troops, causing the Union force to fall back.
By 9:00am the Battle was over. The Federals had sustained 689 casualties, of which 107 dead. Whereas the Confederates realized 207 casualties with 52 killed. Had the Federals captured Battery Lamar they would have flanked the harbor defenses and might have forced the abandonment of Charleston by the Confederacy, cut the Atlantic Coast Line Railroad and established a base for operations into the interior which might have ended the war two years sooner.
B. 1862: CSA Gen. Robert E. Lee orders Maj Gen Thomas Stonewall Jackson to begin plans to leave the Valley to bring his 18,500 men to Richmond. After what had already become a legendary campaign of fighting, deception and hard marching, his force was needed to reinforce the Army of Northern Virginia, protecting the capital from Union General George McClellan’s Army of the Potomac.
C. 1863: Gettysburg Campaign. Come dawn, the true occupation began of Chambersburg, Pennsylvania. CSA Brig Gen Jenkins and his Confederates paid for everything, but three particular items. The first was horses, which he considered contraband of war. When the horses were found to be in short supply, he proceeded to take all of the arms in the town. Any make or model would do. When delivered, he destroyed the worthless and kept the finest.
The third item which Jenkins took while refusing to pay was black people. His men rounded them up like they had wanted to round up horses. Slave, free, man, women, or child, it did not matter. To them, a black person was a slave and nothing more.
D. 1864: The Second Battle of Petersburg, Virginia: June 15-18, 1864
Despite three full Federal corps being present, Winfield Scott Hancock’s II Corps was the only one which made any attacks greater than a demonstration. Confederate Batteries 3, 13, and 14 fell after the 6 pm attacks commenced. However, CSA Gen. P.G.T. Beauregard’s lines had held, and he even made a few local counterattacks that evening to try to regain some ground. These failed, but kept the tired Union soldiers from getting much needed sleep. The odds were not going to get better than this for the Union forces.
Background: Marching from Cold Harbor, Meade’s Army of the Potomac crossed the James River on transports and a 2,200-foot long pontoon bridge at Windmill Point. Butler’s leading elements (XVIII Corps and Kautz’s cavalry) crossed the Appomattox River at Broadway Landing and attacked the Petersburg defenses on June 15. The 5,400 defenders of Petersburg under command of Gen. P.G.T. Beauregard were driven from their first line of entrenchments back to Harrison Creek. The first day of the Second Battle of Petersburg had seen the Confederate defenders driven back from the Dimmock Line to the western bank of Harrison Creek.
After dark the William F. “Baldy” Smith’s XVIII Corps was relieved by the Winfield Scott Hancock’s II Corps. CSA Gen. P.G.T. Beauregard had received reinforcements through the night, with Hoke’s division arriving first, and then Johnson’s division after Beauregard made the decision to strip the Bermuda Hundred lines to the north of all but skirmishers. CSA Gen. Robert E. Lee would have to plug that hole with his Army of Northern Virginia. Over on the Union side, Winfield Scott Hancock’s II Corps had joined Baldy Smith’s XVIII Corps late on the evening of June 15, and the IX Corps joined them late on the morning of the 16th. The Union corps kept expanding the line to the left from the anchor of the Appomattox River, the XVIII Corps on the left, the II Corps in the center, and the IX Corps on the far right. Three Union corps, around 50,000 men, confronted two Confederate divisions, around 14,000 or so.
Hancock had instructed II Corps division commanders Gibbon and Birney to scout the positions in front of them for a dawn attack, but delays prevented this from occurring until 6 am, well after dawn. Gibbon was on the right, Birney in the center, and as Barlow’s division of the II Corps showed up after a frustrating march in which they lost their way, they formed the left of the corps. Lt Gen Ulysses S. Grant conferred with Maj. Gen. George G. Meade, asked him to take charge of the assaults, and asked for an attack by 6 pm on the evening of the 16th.

FYI PV2 Larry Sellnow Maj Bill Smith, Ph.D. SMSgt Lawrence McCarter PO3 Edward Riddle MAJ Roland McDonald CMDCM John F. "Doc" Bradshaw COL (Join to see) SPC Michael Terrell COL Lisandro Murphy LTC Trent Klug CWO3 Dennis M. CPT Kevin McComas]SSgt David M. SPC Maurice Evans SFC Ralph E Kelley
[1864] The Siege of Petersburg
https://www.youtube.com/watch?v=O3KKP-efrOI