On May 1st, Union troops under Benjamin Butler began entering the strategically vital city of New Orleans.
On May 3rd, Confederate General Joseph E. Johnston suddenly withdrew from the Warwick Line in the Battle of Yorktown. The sudden retreat ceded the battle to Union forces under McClellan.
The Battle of Williamsburg was fought on May 5th. This was the first major clash of the Peninsula Campaign, involving around 41,000 Federals and some 32,000 Confederates. Joseph Hooker's Union division encountered the rear guard of Joseph Johnston's Rebel troops fleeing the Battle of Yorktown. This rear guard, Jeb Stuart's cavalry, skirmished with Stoneman's Union horse troopers who had been sent by McClellan after their unexpected withdrawal from Yorktown. Johnston, trying to buy time for his retreat, detached troops to man a large earthen fortification called Fort Magruder, straddling the Yorktown-Williamsburg road. Hooker assaulted the fort, but was repulsed by counterattacks by Confederate General James Longstreet. Hooker was expecting help from William "Baldy" Smith, but Smith, fearing a Confederate attack on his position, held up a little over a mile away. Longstreet's attacks pushed Hooker's troops back. A Union brass band playing "Yankee Doodle" managed to slow the retreat until General Phil Kearny came up with his division. Kearny displayed characteristic dash and daring, riding out in front of the line and urging the Union troops to the attack with a wave of his sword. The Union troops pushed the Confederates back. Winfield Hancock's Union division began an artillery bombardment of Longstreet's left flank, disobeying orders to fall back. After a failed attack by Jubal Early, Hancock's men executed a superb bayonet charge, rolling up the Confederate line. The battle was trumpeted as a major victory by the Northern press, but in reality, Johnston's fight proved to be a delaying action which allowed the bulk of the Confederate army to retreat to Richmond.
On May 7th, they clashed again in the Battle of Eltham's Landing. This time Union troops under William Franklin tried to attack the Barhamsville Road, attempting to disrupt the Confederate retreate from Williamsburg. The Rebels successfully resisted the attack and continued their retreat.
May 8th saw the Battle of McDowell in the Shenandoah. Stonewall Jackson pushed Union troops under Schenk and Milroy off of a strategic ridge after a fierce and bloody fight, setting the stage for Jackson's successful Valley Campaign.
Union General David Hunter freed the slaves in South Carolina, Florida, and Georgia on May 9th. On that same day, Confederate troops destroyed military facilities at Norfolk before continuing their retreat down the peninsula.
On May 10th, Confederate ships clashed with a Union squadron consisting of several ironclads and mortar boats. The Confederate ships defeated the Union force, actually sinking two of the ironclads, but were unable to prevent the Union navy from proceeding down river towards Memphis, Tennessee.