Battle of Beaver Dam Creek The Battle of Beaver Dam Creek , also known as the Battle of Mechanicsville or Ellerson ' s Mill , took place on June 26 , 1862 , in Hanover County , Virginia , as the first major engagement of the Seven Days Battles during the Peninsula Campaign of the American Civil War . It was the start of Confederate General Robert E . Lee ' s counter - offensive against the Union Army of the Potomac , under Maj . Gen . George B . McClellan , which threatened the Confederate capital of Richmond . Lee attempted to turn the Union right flank , north of the Chickahominy River , with troops under Maj . Gen . Thomas J . " Stonewall " Jackson , but Jackson failed to arrive on time . Instead , Maj . Gen . A . P . Hill threw his division , reinforced by one of Maj . Gen . D . H . Hill ' s brigades , into a series of futile assaults against Brig . Gen . Fitz John Porter ' s V Corps , which occupied defensive works behind Beaver Dam Creek . Confederate attacks were driven back with heavy casualties . Porter withdrew his corps safely to Gaines Mill . Background and Lee ' s plan . After the Battle of Seven Pines , on May 31 and June 1 , McClellan and the Army of the Potomac sat passively at the outskirts of Richmond for almost a month . Lee , newly appointed commander of the Confederate Army of Northern Virginia , devoted this period to reorganizing his army and preparing a counter - attack . He also sent for reinforcements . Stonewall Jackson arrived on June 25 from the Shenandoah Valley following his successful Valley Campaign . He brought four divisions : his own , now commanded by Brig . Gen . Charles S . Winder , and those of Maj . Gen . Richard S . Ewell , Brig . Gen . William H . C . Whiting , and Maj . Gen . D . H . Hill The Union Army straddled the rain - swollen Chickahominy River . Four of the Army ' s five corps were arrayed in a semicircular line south of the river . The V Corps under Brig . Gen . Porter was north of the river near Mechanicsville in an L - shaped line running north - south behind Beaver Dam Creek and southeast along the Chickahominy . Lee moved most of his army north of the Chickahominy to attack the Union north flank . He left only two divisions ( under Maj . Gens . Benjamin Huger and John B . Magruder ) to face the Union main body . This concentrated about 65 , 000 troops against 30 , 000 , leaving only 25 , 000 to protect Richmond against the other 60 , 000 men of the Union army . It was a risky plan that required careful execution , but Lee knew that he could not win in a battle of attrition or siege against the Union army . The Confederate cavalry under Brig . Gen . J . E . B . Stuart had reconnoitered Porter ' s right flank as part of a daring , circumnavigation of the entire Union army from June 12 to June 15 and found it vulnerable . Stuart ' s forces burned a couple of Union supply ships and was able to report much of McClellan ' s army ' s strength and position to Gen . Lee . McClellan was aware of Jackson ' s arrival and presence at Ashland Station , but did nothing to reinforce Porter ' s vulnerable corps north of the river . Lee ' s plan called for Jackson to begin the attack on Porter ' s north flank early on June 26 . Maj . Gen . A . P . Hill ' s Light Division was to advance from Meadow Bridge when he heard Jackson ' s guns , clear the Union pickets from Mechanicsville , and then move to Beaver Dam Creek . The divisions of Maj . Gens . D . H . Hill and James Longstreet were to pass through Mechanicsville , D . H . Hill to support Jackson and Longstreet to support A . P . Hill . Lee expected Jackson ' s flanking movement to force Porter to abandon his line behind the creek , and so A . P . Hill and Longstreet would not have to attack Union entrenchments . South of the Chickahominy , Magruder and Huger were to demonstrate , deceiving the four Union corps on their front . Battle . 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 : a frontal assault with 11 , 000 men . Brig . Gen . George A . McCall ' s Union division was forced back . Porter reinforced McCall with the brigades of Brig . Gens . John H . Martindale and Charles Griffin , and extended and strengthened his right flank . He fell back and concentrated along Beaver Dam Creek and Ellerson ' s Mill . 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 bivouac for the evening . A . P . Hill , now with Longstreet and D . H . Hill behind him , continued his attack , despite orders from Lee to hold his ground . His assault was beaten back with more casualties . Jackson did not attack , but his presence near Porter ' s flank caused McClellan to order Porter to withdraw after dark behind Boatswain ' s Swamp , five miles ( 8 km ) to the east . McClellan was concerned that the Confederate buildup on his right flank threatened his supply line , the Richmond and York River Railroad north of the Chickahominy , and he decided to shift his base of supply to the James River . ( He also believed that the demonstrations by Huger and Magruder showed that he was seriously outnumbered . ) This was a strategic decision of grave import because it meant that , without the railroad to supply his army , he had to abandon his siege of Richmond . Aftermath . Overall , the battle was a Union tactical victory , in which the Confederates suffered heavy casualties and achieved none of their specific objectives due to the seriously flawed execution of Lee ' s plan . Instead of over 60 , 000 men crushing the enemy ' s flank , only five brigades , about 15 , 000 men , had seen action . Their losses were 1 , 484 versus Porter ' s 361 . Lee ' s staff recalled that he was " deeply , bitterly disappointed " by Jackson ' s performance , but communication breakdowns , poorly written orders from Lee , and bad judgment by most of Lee ' s other subordinates were also to blame . Despite the Union tactical success , however , it was the start of a strategic debacle and the unraveling of the Peninsula Campaign . McClellan began to withdraw his army to the southeast and never regained the initiative . The next day the Seven Days Battles continued as Lee attacked Porter at the Battle of Gaines ' Mill .