Lee's intricate plan went awry immediately.
Jackson's men, fatigued from their recent campaign and lengthy march, ran at least four hours behind schedule.
By 3 p.m., A.P. Hill grew impatient and began his attack without orders.
Hill's division, minus Brig.
Gen Lawrence O'Brian Branch's brigade, which was placed off to the north to link up with Jackson, entered Mechanicsville and skirmished with George McCall's Union division, deployed around the town.
McCall fell back to an easily defensible spot on the opposite side of Beaver Dam Creek.
There, the brigades of Brig.
Gen John F. Reynolds and Brig.
Gen Truman Seymour dug in, with Brig.
Gen George G. Meade's brigade placed behind them in reserve, Reynolds' brigade to the north and Seymour's to the south.
On Reynolds' right, the divisions of Brig.
Gen George Morell and Brig.
Gen George Sykes formed a semicircle.
Supporting the roughly 26,000 Union infantrymen were 32 artillery pieces.
There, 14,000 well entrenched infantry, supported by 32 guns in six batteries, repulsed repeated Confederate attacks with substantial casualties.

Jackson and his command arrived late in the afternoon.
However, unable to find A.P. Hill or D.H. Hill, Jackson did nothing.
Although a major battle was raging within earshot, he ordered his troops to make camp for the evening.
Hill's 11,000 men, most of them green regiments who had never fired a shot in battle, launched a series of futile attacks over the next few hours.
The brigade of John R. Anderson assaulted the Union right flank, with James Archer's and Charles W. Field's brigades in support.
Maxcy Gregg's brigade was held in reserve and did not participate in the battle at all.
Directing his troops, John Reynolds gestured at the oncoming mass of Confederates and told a staffer "There they come like flies on a piece of gingerbread."
The Union artillery and musketry tore enormous gaps in the Confederate lines as they attempted to cross the creek.
Although A.P. Hill had 24 guns with him, he made no attempt to use massed artillery fire to counter the Union gunners, instead sending individual batteries in support of the infantry, most of which were quickly put out of action by enemy shelling.

Some of Anderson's men managed to get across the creek and momentarily threaten Reynolds's position, however he was reinforced by Meade's brigade and two regiments from Morell's division.
The three Confederate brigades were driven back with substantial casualties.
Arriving on the field and realizing what was happening, Robert E. Lee hastily summoned Longstreet's and D.H. Hill's divisions.
As Lee surveyed the futile attacks, Jefferson Davis and the Confederate cabinet rode up to him.
Davis asked him "General, what is all this army and what is it doing here?"
Lee replied sarcastically "I don't know, Mr. President.
It is not my army and this is no place for it."
William D. Pender's brigade then attacked the Union left flank at Ellerson's Mill, held by Seymour's brigade.
Once again, the well-entrenched infantry and massed artillery proved too much for the Confederates and Pender was forced to retreat.
Just then, Roswell Ripley's brigade of D.H. Hill's division arrived on the field and was ordered next to assault the Union left.
Ripley charged head-on into the Union entrenchments and suffered the very worst of all with over 600 casualties, the largest percentage of them coming from the 44th Georgia, which lost 335 men and most of its officers (out of a total of 514), including its colonel Robert A. Smith, a roughly 65% casualty rate.
The 1st North Carolina suffered 50% casualties (133 men killed, wounded, or captured) and also lost its commander, Col.
Montford Stokes.
General Ripley himself survived unscathed, but came within inches of being decapitated by an artillery shell.
Ripley's other two regiments, the 3rd North Carolina and 48th Georgia, were to the rear of the 1st North Carolina and 44th Georgia; their losses were lighter.
Union casualties around Ellerson's Mill were small, only 40 men total were killed or wounded in the 7th Pennsylvania Reserves and 12th Pe
Lee's intricate plan went awry immediately. Jackson's men, fatigued from their recent campaign and lengthy march, ran at least four hours behind schedule. By 3 p.m., A.P. Hill grew impatient and began his attack without orders. Hill's division, minus Brig. Gen Lawrence O'Brian Branch's brigade, which was placed off to the north to link up with Jackson, entered Mechanicsville and skirmished with George McCall's Union division, deployed around the town. McCall fell back to an easily defensible spot on the opposite side of Beaver Dam Creek. There, the brigades of Brig. Gen John F. Reynolds and Brig. Gen Truman Seymour dug in, with Brig. Gen George G. Meade's brigade placed behind them in reserve, Reynolds' brigade to the north and Seymour's to the south. On Reynolds' right, the divisions of Brig. Gen George Morell and Brig. Gen George Sykes formed a semicircle. Supporting the roughly 26,000 Union infantrymen were 32 artillery pieces. There, 14,000 well entrenched infantry, supported by 32 guns in six batteries, repulsed repeated Confederate attacks with substantial casualties.
Jackson and his command arrived late in the afternoon. However, unable to find A.P. Hill or D.H. Hill, Jackson did nothing. Although a major battle was raging within earshot, he ordered his troops to make camp for the evening. Hill's 11,000 men, most of them green regiments who had never fired a shot in battle, launched a series of futile attacks over the next few hours. The brigade of John R. Anderson assaulted the Union right flank, with James Archer's and Charles W. Field's brigades in support. Maxcy Gregg's brigade was held in reserve and did not participate in the battle at all. Directing his troops, John Reynolds gestured at the oncoming mass of Confederates and told a staffer "There they come like flies on a piece of gingerbread." The Union artillery and musketry tore enormous gaps in the Confederate lines as they attempted to cross the creek. Although A.P. Hill had 24 guns with him, he made no attempt to use massed artillery fire to counter the Union gunners, instead sending individual batteries in support of the infantry, most of which were quickly put out of action by enemy shelling.
Some of Anderson's men managed to get across the creek and momentarily threaten Reynolds's position, however he was reinforced by Meade's brigade and two regiments from Morell's division. The three Confederate brigades were driven back with substantial casualties. Arriving on the field and realizing what was happening, Robert E. Lee hastily summoned Longstreet's and D.H. Hill's divisions. As Lee surveyed the futile attacks, Jefferson Davis and the Confederate cabinet rode up to him. Davis asked him "General, what is all this army and what is it doing here?" Lee replied sarcastically "I don't know, Mr. President. It is not my army and this is no place for it." William D. Pender's brigade then attacked the Union left flank at Ellerson's Mill, held by Seymour's brigade. Once again, the well-entrenched infantry and massed artillery proved too much for the Confederates and Pender was forced to retreat. Just then, Roswell Ripley's brigade of D.H. Hill's division arrived on the field and was ordered next to assault the Union left. Ripley charged head-on into the Union entrenchments and suffered the very worst of all with over 600 casualties, the largest percentage of them coming from the 44th Georgia, which lost 335 men and most of its officers (out of a total of 514), including its colonel Robert A. Smith, a roughly 65% casualty rate. The 1st North Carolina suffered 50% casualties (133 men killed, wounded, or captured) and also lost its commander, Col. Montford Stokes. General Ripley himself survived unscathed, but came within inches of being decapitated by an artillery shell. Ripley's other two regiments, the 3rd North Carolina and 48th Georgia, were to the rear of the 1st North Carolina and 44th Georgia; their losses were lighter. Union casualties around Ellerson's Mill were small, only 40 men total were killed or wounded in the 7th Pennsylvania Reserves and 12th Pe
Battle of Beaver Dam Creek