What was the most significant event on April 7 during the U.S. Civil War?

Today marked the high water mark of casualties in the Civil War at Shiloh in 1862. The carnage would go on for three more years. The war in the west was being won by the Union on the water and on the land. In the east GEN Lee and the Army of Northern, VA were able to hold back the Union armies and win a few battles until the end of the war in April 1865.
Since RallyPoint truncates survey selection text I am posting events that were not included and then the full text of each survey choice below:
A. Wednesday, April 7, 1861: CSA Gen P. G. T. Beauregard orders all transports to Fort Sumter cut off. This ended the fort's supply of fresh food.
http://blueandgraytrail.com/year/186104
B. Monday, April 7, 1862: Battle of Shiloh concludes. Two days of heavy fighting conclude near Pittsburgh Landing in western Tennessee. The Battle of Shiloh became a Union victory after the Confederate attack stalled on April 6, and fresh Yankee troops drove the Confederates from the field on April 7.
General Ulysses S. Grant was joined by the vanguard of Buell’s army. With an advantage in terms of troop numbers, Grant counterattacked on April 7. The tired Confederates slowly retreated, but they inflicted heavy casualties on the Yankees. By nightfall, the Union had driven the Confederates back to Shiloh Church, recapturing grisly reminders of the previous days’ battle such as the Hornets’ Nest, the Peach Orchard, and Bloody Pond. The Confederates finally limped back to Corinth, thus giving a major victory to Grant.
C. Tuesday, April 7, 1863: Battle of Charleston Harbor, South Carolina –– Admiral Samuel Du Pont and his fleet of nine Union ironclads sortie into Charleston Harbor in order to capture Fort Sumter in the afternoon. Beauregard’s well-designed defensive battery emplacements at Sumter and Fort Moultrie in the harbor have a dominating overlapping field of fire on every spot in the channel: therefore, Rebel heavy artillery rains down a monsoon of shot and shell on the Yankee ships. Mostly ironclad, the Union ships withstand the battering at first, but the USS Passaic, a double-turret monitor, is disabled, and the USS Keokuk is badly damaged in a similar way---at one point.
The U.S.S. Weehawken was struck 53 times in forty minutes, the U.S.S. Passaic 35 times, U.S.S. Montauk 47 times, U.S.S. Nantucket 51 times, U.S.S. Patapsco 47 times while other vessels were similarly hit and damaged. Confederates threw 2,209 shells compared to just 154 from the ironclads. Battered by the forts and endangered by obstruction and torpedoes, the Federal fleet withdrew with five disabled vessels. The U.S.S. Keokuk, hit 90 times, sunk the next morning.
Confederate Victory. US Naval occupation of the harbor is ruled out.
D. Tuesday, April 7, 1863: Commodore Andrew Foote runs the USS Carondelet past the Rebel batteries at Island No. 10, and makes it safely to New Madrid. After another gunboat accomplishes the same thing, then Gen. John Pope ferries his troops safely downstream and lands them south of the fortress at Island No. 10, cutting off the Rebel garrison from retreat. Rebel Gen. Wm. Mackall will surrender formally on the morrow, with 4,500 Confederate troops as prisoners of the Union
1. Wednesday, April 7, 1861: Confederate Commissioners Telegrams
During March and April 1861, after seven states had seceded and formed the Confederate States of America but before war broke out, Confederate Secretary of State Robert Toombs appointed Martin J. Crawford, John Forsyth, and A.B. Roman as Commissioners of the Confederate States to Washington, DC. Their purpose was to seek diplomatic recognition from the United States and negotiate peace—at least for a while. Central to the question of peace or war was whether the United States would continue to retain claim over federal forts located in the southern states that had seceded, including Fort Pickens in Florida and Fort Sumter in South Carolina. This item is transcribed from a letter book maintained by J.T. Pickett, secretary to the commissioners, containing copies of 72 letters, dispatches, and telegrams sent and received by the commissioners from the time of their appointment to the demand for the evacuation of Fort Sumter.
4-7-1861 telegram Washington April 7th 1861.To Hon R Toombs.
Events since our last have in our judgment made it our duty to require an answer to our official note of March Twelfth—We do so tonight with notification that our Sec’ty will call for a reply tomorrow at two PM—We believe that a hostile movement is on foot and part of it sailed against the confederate states—It may be Sumter and [inserted: or] the Mississippi—It is almost certain that it is Pickens and the Texas frontier—If Sewards reply is not satisfactory we shall consider the gauntlet of war thrown down—and close our mission after two P.M . tomorrow will teleg’h you.
Crawford Roman & Forsyth.
4-7-1861 telegram To Hon Mess. Crawford & Forsyth, Commissioners
We have so many extraordinary telegrams I would be glad to know from you if it is true that they have determined to reinforce Sumter & if a naval force is sent to our harbor.
Be so good as to answer as soon as convenient for something desired to govern our conduct.
F. W. Pickens.
Citation: Commissioners of the Confederate States of America to the Government of the United States, letter book. Washington, D.C., Feb 27-April 11, 1861.AMS 811/20
2. Monday, April 7, 1862: Battle of Pittsburg Landing [Union]; Battle of Shiloh [Confederate]. Ulysses S. Grant [US] defeats Albert Sidney Johnston [CS] in southwest Tennessee. P. G. T. Beauregard assumed command following Johnston's death
Confederate Losses: 1,723 dead; 8,012 wounded; 959 missing
Union Losses: 1,754 dead; 8,408 wounded; 2,885 missing
http://blueandgraytrail.com/year/186204
3. Monday, April 7, 1862: Western Theater, Tennessee Valley Campaign - THE BATTLE OF SHILOH, Tennessee. Day Two. All night, transports ferry across the river the rest of Buell’s troops that are present–in addition to Nelson’s Division, there are also division under McCook, Crittenden, and Wood. Grant plans to counterattack. Buell’s Army of the Ohio takes the left part of the Union line, while Grant’s army takes the right flank. Due to bad blood between Grant and Buell, the two commanders decided to each command their own troops in cooperation. Hurlbut, McClernand, and Sherman’s divisions extend from the center to the right, where Lew Wallace’s division took its place at the extreme right flank.
The Confederate army scattered, disorganized, and beyond any command structure, this morning Beauregard faces the huge task of getting them organized to resume the attacks. His goal is to press Grant and force a surrender, but he has no idea that Buell has arrived and has crossed the river, even though many of his troops and officers know, so shabby are staff communications in this army. Nelson’s division steps off first, and advances. The Rebels do not even respond until Nelson is nearly on them—then they respond and begin to form a resistance. The rest of the Union line steps off, and Grant finds little resistance in front of him. The Army of the Tennessee moves a full mile and a half before encountering any resistance. Buell, however, has stalled, and the fighting breaks up into small battles with clumps of disorganized Confederates. The Rebels begin falling back, however, as Beauregard realizes that he has no choice but to retreat. He places Breckenridge’s Reserves near Shiloh Church to slow down the Yankee advance until he can get the rest of the army safely on the road to Corinth. Union Victory.
Losses: Killed Wounded Captured or Missing Total
U.S. 1,754 8,408 2,885 13,047
C.S. 1,728 8,012 959 10,699
4. Shiloh was, to date, the bloodiest recorded battle fought in North America. Patrick Cleburne’s Arkansas and Tennessee division went into battle with 2750 men. At the end of the battle, he had only 58 left.
http://civilwarsesquicentdaily-wolfshield.blogspot.com/search?q=April+7%2C+1862
5. Monday, April 7, 1862 --- Private Sam. R. Watkins, of the 1st Tennessee Infantry, who fought at Shiloh, records his memory of the Southern fortunes that day: On Monday the tide was reversed. Now, those Yankees were whipped, fairly whipped, and according to all the rules of war they ought to have retreated. But they didn't. Flushed with their victories at Fort Henry and Fort Donelson and the capture of Nashville, and the whole State of Tennessee having fallen into their hands, victory was again to perch upon their banners, for Buell's army, by forced marches, had come to Grant's assistance at the eleventh hour.
Gunboats and transports were busily crossing Buell's army all of Sunday night. We could hear their boats ringing their bells, and hear the puff of smoke and steam from their boilers. Our regiment was the advance outpost, and we saw the skirmish line of the Federals advancing and then their main line and then their artillery. We made a good fight on Monday morning, and I was taken by surprise when the order came for us to retreat instead of advance. But as I said before, reader, a private soldier is but an automaton, and knows nothing of what is going on among the generals, and I am only giving the chronicles of little things and events that came under my own observation as I saw them then and remember them now. Should you desire to find out more about the battle, I refer you to history.
http://civilwarsesquicentdaily-wolfshield.blogspot.com/search?q=April+7%2C+1862
6.
7. Thursday, April 7, 1864: On this date, CSA Lt. Gen. James Longstreet and his divisions in East Tennessee are ordered to move back to Virginia, after seven months in Tennessee and Georgia, to join again with Gen. Lee’s Army of the Northern Virginia.
http://civilwarsesquicentdaily-wolfshield.blogspot.com/search?q=April+7%2C+1864
8. April 7, 1865: Battle of High Bridge, VA
Background
High Bridge, 2,500 feet (760 m) long and 126 feet (38 m) high, was the crossing of the South Side Railroad over the Appomattox River and its flood plain, 4 miles (6.4 km) northeast of Farmville, Virginia.[6] A wooden bridge for wagons was located below the railroad bridge. During the retreat of Confederate General Robert E. Lee's Army of Northern Virginia during the Appomattox Campaign, the Confederates had moved north of the river, except for a rear guard provided by Longstreet's First Corps at Rice's Station on the southern bank. The bridges had to be protected on April 6 and then destroyed on April 7 to delay the pursuit of the Confederates by the Union Army (Army of the Potomac, Army of the James and Army of the Shenandoah) under Lieutenant General Ulysses S. Grant.
On April 6, Longstreet dispatched 1,200 Confederate cavalry under Major General Thomas L. Rosser to protect the bridges from Union raiders. Union Major General Edward Ord, commanding the Army of the James, sent about 900 men under Colonel (Brevet Brigadier General) Theodore Read (Ord's chief of staff) to burn the bridge. This force consisted of the 123rd Ohio Infantry and the 54th Pennsylvania Infantry, commanded by Lieutenant Colonel Horace Kellogg of the 123rd Ohio, and three companies (80 troopers) of the 4th Massachusetts Cavalry under Colonel Francis Washburn. The cavalry reached the bridge before the main Confederate force, chased away some poorly armed home guards, and secured the south end of the bridge.
Battles
While Washburn prepared to set fire to the bridge, three brigades of Confederate cavalrymen arrived and conducted a dismounted attack against the Union infantry, which was waiting near the Watson farmhouse, about half mile to the south. Hearing sounds of battle, Washburn and his men rejoined the infantry, and unaware that he was facing two divisions of cavalry, Read ordered a mounted charge by the 4th Massachusetts. The ferocious charge forced through the Confederate line of Brigadier General Thomas T. Munford and dissolved into hand-to-hand combat. Read exchanged gunfire with Confederate James Dearing during the fighting and was killed. Dearing was mortally wounded and died on April 22. Washburn was also mortally wounded. The Confederates counterattacked and separated the cavalry from their supporting infantry. After another attack, the Union troopers were surrounded, and all were killed, wounded, or captured. Colonel Reuben B. Boston of the 5th Virginia Cavalry was killed in the attack.
The survivors of the Confederate Second Corps, under Major General John B. Gordon, escaped from their defeat at the Battle of Sailor's Creek and crossed the High Bridge to the north side of the river while Major General William Mahone's division secured the bridge. The rest of Lee's army moved on to Farmville and a rendezvous with trains of rations.
Early on April 7, while Mahone's men were attempting to set fire to the High Bridge and wagon bridge, the Union II Corps commanded by Major General Andrew A. Humphreys arrived on the scene. Humphreys's second division under Brigadier General Francis C. Barlow, including the 19th Maine Volunteer Infantry Regiment, charged the burning structure and saved a large section of the railroad bridge, preventing major damage. They crossed the lower wagon bridge to move on Lee's flank and forced the hungry Confederates to resume their retreat before re-provisioning themselves.
Aftermath
Together, the battles at High Bridge were tactically inconclusive, despite the 847 Union casualties (including 800 captured) versus only about 100 Confederate in the first battle. Lee was forced to continue his march to the west under pressure, depriving some of his men the opportunity to eat the Farmville rations they had waited so long to receive. Their next stop would be Appomattox Station, 25 miles (40 km) west, where a ration train was waiting.
On the night of April 7, Lee received from Grant a letter proposing that the Army of Northern Virginia should surrender. Lee demurred, retaining one last hope that his army could get to Appomattox Station before he was trapped. He returned a noncommittal letter asking about the surrender terms "Unconditional Surrender" Grant might propose.
https://en.wikipedia.org/wiki/Battle_of_High_Bridge
9. April 7, 1865: Grant and Lee Exchange Letters. On this day the Union pursuit of Lee and the Army of Northern Virginia continued. After the defeat and capture of perhaps a quarter of Lee's army the day before at Sailor's Creek, Grant felt the need to write Lee and ask him to consider surrender.
From Grant's memoirs: I rode in to Farmville on the 7th, arriving there early in the day. Sheridan and Ord were pushing through, away to the south. Meade was back towards the High Bridge, and Humphreys confronting Lee as before stated. After having gone into bivouac at Prince Edward's Court House, Sheridan learned that seven trains of provisions and forage were at Appomattox, and determined to start at once and capture them; and a forced march was necessary in order to get there before Lee's army could secure them. He wrote me a note telling me this. This fact, together with the incident related the night before by Dr. Smith, gave me the idea of opening correspondence with General Lee on the subject of the surrender of his army.
I therefore wrote to him on this day, as follows:
HEADQUARTERS ARMIES OF THE U. S., 5 P.M., April 7, 1865. To GENERAL R. E. LEE Commanding C. S. A.
The result of the last week must convince you of the hopelessness of further resistance on the part of the Army of Northern Virginia in this struggle. I feel that it is so, and regard it as my duty to shift from myself the responsibility of any further effusion of blood, by asking of you the surrender of that portion of the Confederate States army known as the Army of Northern Virginia.
U. S. GRANT, Lieut.-General.
Lee replied on the evening of the same day as follows:
April 7, 1865. To LIEUT.-GENERAL U. S. GRANT, Commanding Armies of the U. S.
GENERAL: I have received your note of this day. Though not entertaining the opinion you express on the hopelessness of further resistance on the part of the Army of Northern Virginia, I reciprocate your desire to avoid useless effusion of blood, and therefore before considering your proposition, ask the terms you will offer on condition of its surrender.
R. E. LEE, General.
http://www.civilwar-online.com/2015/04/april-7-1865-grant-and-lee-exchange.html
10. April 7, 1866: Congress appropriates $100,000 to buy Ford's Theater. It will house the Army Medical Museum, the Office of the Surgeon General and War Department records until 1893.
http://blueandgraytrail.com/year/1866
B. Monday, April 7, 1862 Battle of Shiloh concludes. Two days of heavy fighting conclude near Pittsburgh Landing in western Tennessee. The Battle of Shiloh became a Union victory after the Confederate attack stalled on April 6, and fresh Yankee troops drove the Confederates from the field on April 7.
Shiloh began when Union General Ulysses S. Grant brought his army down the Tennessee River to Pittsburgh Landing in an effort to move on Corinth, Mississippi, 20 miles to the southwest. Union occupation of Corinth, a major rail center, would allow the Yankees to control nearly all of western Tennessee. At Corinth, Confederate General Albert Sidney Johnston did not wait for Grant to attack. He moved his army toward Grant, striking on the morning of April 6. Throughout the day, the Confederates drove the Yankees back but could not break the Union lines before darkness halted the advance. Johnston was killed during the first day, so General Pierre G. T. Beauregard assumed command of the Confederate force.
Now, Grant was joined by the vanguard of Buell’s army. With an advantage in terms of troop numbers, Grant counterattacked on April 7. The tired Confederates slowly retreated, but they inflicted heavy casualties on the Yankees. By nightfall, the Union had driven the Confederates back to Shiloh Church, recapturing grisly reminders of the previous days’ battle such as the Hornets’ Nest, the Peach Orchard, and Bloody Pond. The Confederates finally limped back to Corinth, thus giving a major victory to Grant.
The cost of the victory was high. Grant’s and Buell’s forces totaled about 62,000, of which 1,754 were killed, 8,408 were wounded, and 2,885 were captured or missing for a total of 13,047 casualties. Of 45,000 Confederates engaged, 1,723 were killed, 8,012 wounded, and 959 missing for a total of 10,694 casualties. The 23,741 casualties were five times the number at the First Battle of Bull Run in July 1861, and they were more than all of the war’s major battles (Bull Run, Wilson’s Creek, Fort Donelson, and Pea Ridge) to that date combined. It was a sobering reminder to all in the Union and the Confederacy that the war would be long and costly.
http://www.history.com/this-day-in-history/battle-of-shiloh-concludes
B+. Monday, April 7, 1862 Battle of Shiloh concludes
Monday morning, April 7, at daylight, the vanquished of the previous day renewed the struggle with increased strength and restored confidence. Anxious to take the initiative the Union armies were put in motion almost simultaneously, with General Buell on the left, Lew Wallace on the extreme right, and Grant's weary troops occupying the space between. The movement began unopposed, except by small unsupported parties which were quickly forced to retreat.
The Confederates had been unable to reorganize their widely scattered forces during the night. Therefore, when the Union advance began on Monday the opposing line of battle was yet unformed. The Confederates were still back in the vicinity of the captured Union camps vainly trying to reorganize their broken commands. They did not succeed in forming a line until after the enemy had advanced beyond the Peach Orchard and the Hornets' Nest, regaining much of the territory they had lost the day before.
The Confederates, one brigade strong, were first encountered by Lew Wallace a short distance in front of his Sunday night bivouac. In a brief but spirited engagement, the Confederates were attacked in front and on the left flank by the Union division. To keep from being surrounded, they fell back almost a mile in the direction of Shiloh Church to take their place in the forming line of battle.
In the meantime, Buell moved his troops rapidly forward until they developed the Confederate line of battle west of the Peach Orchard. The Southerners boldly charged the advancing Union infantry which had moved forward so rapidly that its artillery was still far to the rear. Without artillery support, the Federals were unable to withstand the violent assault of the Confederates and were forced to make a hasty retreat. The timely arrival and effective use of two batteries of artillery permitted the Union line again to advance, only to be driven back once more by the stubborn Confederates.
The battle now raged the entire length of the field. Charge followed by countercharge moved the fitfully swaying line first toward the river and then toward the church. The advantage would seem to test momentarily with the weary Southerners, but would soon be lost to their greatly strengthened opponent. Commands became so intermingled and confused that it was often impossible to distinguish between friend and foe. The Confederates, clad in a variety of colored uniforms, with no well-defined line and on an ever-changing front, suffered the heavier losses from the fire of their own troops.
Meanwhile, General Beauregard, at Shiloh Church, anxiously awaited the return of couriers he had dispatched to Corinth to hurry forward General Earl Van Dorn's army of about 20,000 men, daily expected there from Van Buren, Ark. He had promised to make a junction with General Beauregard as soon as possible, but was delayed because he had no means of transporting his troops across the Mississippi. Unaware that Van Dorn was still in Arkansas, General Beauregard maintained his largest troop concentration in the vicinity of the church to defend the Corinth-Pittsburg Road so that reinforcements could be quickly moved onto the field. As soon as it became known that additional troops were not on the way, Beauregard realized that the road would have to be kept open as a possible line of retreat. The Union commanders were equally determined to drive the Confederates from the position. Consequently, furious fighting raged before the church long after the tempo of the battle had slackened on each flank.
Despite all efforts of the Confederates, the Union line continued slowly to advance. In desperation the Confederates made a gallant charge, first expending their ammunition and then relying on the bayonet. The charge carried the surging line through waist-deep Water Oaks Pond, beyond which the fire from the adversary became so strong that the line was brought to an abrupt halt. Taking cover at the edge of a woods, they repulsed every attempt by the Federals to advance.
By 2 p. m. General Beauregard decided it was useless to prolong the unequal struggle. Since early morning, his lines had been forced back, step by step, with heavy losses. From all parts of the field his subordinates were sending urgent requests for reinforcements, which he was unable to supply. Even his position at the church was in danger of being taken. A continuation of the battle could bring only additional disasters upon his already greatly depleted ranks. To forestall a complete rout, he ordered a rear guard with artillery support to be put in position on the ridge west of the church and instructed his corps commanders to begin withdrawing their troops. By 4 o'clock, the last of the Confederate Army, or what was left of it, had retired from the field and was leisurely making its way back to Corinth without a single Federal soldier in pursuit.
The Union armies did not attempt to harass the retreating Southern columns or attack them when they went into bivouac for the night. Instead, Grant's troops, from the privates to the highest commanders, appear to have been content to return to their recaptured camps, while the Confederates returned to their former positions in and around Corinth to recruit and reorganize.
In explanation of his inactivity Grant said: "My force was too much fatigued from two days' hard fighting and exposure in the open air to a drenching rain during the intervening night, to pursue immediately. Night closed in cloudy and with heavy rain, making roads impracticable for artillery by the next morning."
The next morning, April 8, however, General Thomas J. Wood, with his division, and Sherman, with two brigades and the 4th Illinois Cavalry, went in pursuit. Toward evening they came upon the Confederate rear guard at Fallen Timbers, about 6 miles from the battlefield. The Southern cavalry, commanded by Colonel Nathan Bedford Forrest, charged the Federals, putting the skirmishers to flight and throwing the Union cavalry into confusion. The Confederates, pursuing too vigorously, came suddenly upon the main body of Federal infantry and were repulsed, after Colonel Forrest had been seriously wounded in the side. Before returning to camp, the Northerners tarried long enough to bury their 15 dead, gather up their 25 wounded, and find out that they had lost 75 as prisoners. The spirited action of the Confederate rear guard at Fallen Timbers put an end to all ideas of further pursuit by the Federals.
http://www.americancivilwar.com/Shiloh_Tennessee_2.html
C. Tuesday, April 7, 1863: Battle of Charleston Harbor, South Carolina – Admiral Samuel Du Pont and his fleet sortie into Charleston Harbor in order to capture Fort Sumter. Beauregard’s well-designed defensive battery emplacements in the harbor have a dominating overlapping field of fire on every spot in the channel: therefore, Rebel heavy artillery rains down a monsoon of shot and shell on the Yankee ships. Mostly ironclad, the Union ships withstand the battering at first, but the USS Passaic, a double-turret monitor, is disabled, and the USS Keokuk is badly damaged in a similar way---at one point, Keokuk fired only three shots to the ninety shots that struck her. Her turrets inoperable, the Keokuk drifts out of action. Du Pont finally calls off the debacle and orders a withdrawal. The Weehawken, the Montauk, the Patapsco, and the Nantucket are all badly hit, also. Confederate Victory.
http://civilwarsesquicentdaily-wolfshield.blogspot.com/search?q=April+7%2C+1863
C+. Tuesday, Tuesday April 7, 1863
Nine Federal ironclads under Flag Officer Samuel DuPont steamed into Charleston Harbor and attacked Fort Sumter in the afternoon. Both Sumter and Fort Moultrie returned the fire. The U.S.S. Weehawken was struck 53 times in forty minutes, the U.S.S. Passaic 35 times, U.S.S. Montauk 47 times, U.S.S. Nantucket 51 times, U.S.S. Patapsco 47 times while other vessels were similarly hit and damaged. Confederates threw 2,209 shells compared to just 154 from the ironclads. Battered by the forts and endangered by obstruction and torpedoes, the Federal fleet withdrew with five disabled vessels. The U.S.S. Keokuk, hit 90 times, sunk the next morning.
http://mncivilwar150.com/2013/03/
C+ April 7, 1863: The First Battle of Charleston Harbor. On this day 150 years ago, nine Union ironclads steamed into Charleston, South Carolina's harbor in hopes of forcing the city into capitulating. Instead, they found that they had stuck their arms into a hornets' nest.
FORT SUMTER, April 7, 1863. Have visited Fort Sumter. One 10-inch gun carriage and chassis disabled; one 8-inch burst; two rifled dismounted and now replaced; walls badly shaken in two or three places; 4 men badly wounded. The engineers should look out and have material and laborers for repairs as soon as possible. Colonel Rhett, Lieutenant-Colonel Yates, and Major Blanding are doing all that can be done to repair. Do send us something for sand bags to fortify shaken places--if the people send their petticoats and pillow-cases--at once. One steamer should be sent down with what can be furnished to carry ammunition to Morris Island. Some of the enemy have been badly hurt. The Keokuk is probably for sale. Whether the attack will be renewed or not I cannot judge; the probability is that it will, and the men will shoot better tomorrow than to-day. The big torpedo did not explode; I do not know why. Shall go to Morris Island in an hour or so and find out. I don't think we had better say it is over, but will let you know in the morning.
R.S. RIPLEY.
Brigadier General JORDAN. The "big torpedo" Ripley mentioned was a 3,000 lb. mine that the U.S.S. New Ironsides had anchored over. The wires that controlled the mine had been buried too shallow, and a passing wagon had broken the wires, thus costing the Confederacy a major victory.
Charleston's defenses boasted no fewer than 385 cannon, but many of those cannon were too small to damage an ironclad and the Confederates didn't bother firing these weapons at the federal ironclads. The Confederates kept a detailed record of the guns that fired at the federal ironclads (see below)
The Confederacy had learned its lesson at New Orleans and Fort Donelson. The defenses of Charleston included many powerful heavy cannon that were capable of punishing, if not penetrating, federal ironclads.
http://www.civilwar-online.com/2013/04/april-7-1863-first-battle-of-charleston.html
D. Monday, April 7, 1862 --- Commodore Andrew Foote runs the USS Carondelet past the Rebel batteries at Island No. 10, and makes it safely to New Madrid. After another gunboat accomplishes the same thing, then Gen. John Pope ferries his troops safely downstream and lands them south of the fortress at Island No. 10, cutting off the Rebel garrison from retreat. Rebel Gen. Wm. Mackall will surrender formally on the morrow, with 4,500 Confederate troops as prisoners of the Union.
http://civilwarsesquicentdaily-wolfshield.blogspot.com/search?q=April+7%2C+1862
FYI LTC Stephen C. LTC (Join to see) CSM Charles Hayden SFC William Swartz Jr SPC (Join to see) 1stSgt Eugene Harless CPT Kevin McComas SPC Maurice Evans SFC Ralph E Kelley LTC Trent Klug MSgt James ParkerLTC John Griscom MAJ (Join to see) SMSgt David A Asbury SPC James Neidig2022 1LT (Join to see) SPC Jon O.SSG (Join to see) Maj Bill Smith, Ph.D.

The Union Prevails at the Battle of Shiloh | Civil War Combat (S1, E1) | Full Episode
https://www.youtube.com/watch?v=PJFYfz9H4KU

LTC Stephen F., I really enjoy your discussion threads regarding the War of Northern Aggression. However, some of these dates have meaning for me otherwise, so that's why I keep hijacking them!
On April 7, 1970, I made my first jump onto Fryar DZ at Fort Benning, leaping from a C-119. So, April 7th is important to me, only a 107 to 109 years later!

Great post LTC Stephen F.

I thought Shiloh would be the most significant loss of life therefore the most significant event on April 7.

LTC Stephen F. Too many significant events to say one trumps another. Cutting off supplies at the time would have impacted civilian populations as much as military populations within the fort. Shiloh, huge casualties including the highest ranking officer to lose their life in combat during the war. Riverine fighting is a sample of things to come one hundred years later on the rivers of Vietnam. Surrender talk, well that is a sign that formal hostilities are coming to a close. The battle of Charleston Harbor showed that while the Ironclads would do well against other Ironclads, they could be defeated by heavy volume of fire. Cutting of escape, then marching troops in leaves them with the option to surrender, or be obliterated. So yeah I am voting all of the above.