At the Battle of Mechanicsville, Virginia, Confederate General Robert E. Lee’s Army of Northern Virginia strikes Union General George B. McClellan’s Army of the Potomac, beginning the Seven Days’ Battles. Although the Confederates sustained heavy losses and did not succeed in decisively defeating the Yankees, the battle had unnerved McClellan. During the next week, Lee drove him from the outskirts of Richmond, Virginia, back to his base on the James River.

This was Lee’s first battle as commander of the army. On June 1, 1862, he had replaced Joseph Johnston, who was severely wounded at the Battle of Fair Oaks. McClellan’s offensive had stalled just five miles from Richmond, and his army remained there until late June. During that time, General J.E.B. Stuart and his Rebel cavalry made a spectacular ride around McClellan’s force, bringing back information that indicated that McClellan’s right flank was “in the air,” or unprotected by natural barriers. Lee informed his commanders on June 23 of his intention to attack the flank, occupied by Fitz John Porter’s V corps, which was separated from the rest of the Union army by the Chickahominy River. This was a bold move–because it meant leaving a skeleton force to face the rest of McClellan’s army south of the Chickahominy—and an early indication of Lee’s audacious style.

But the attack did not go as planned. McClellan, alerted to the vulnerability of his flanks by Stuart’s ride two weeks prior, had shored up his left, and moved Porter’s men to high ground with a deep creek in front of them. Lee’s plan had called for several smaller forces to overwhelm Porter’s men, but it required precise timing. When the assault came, the coordination did not materialize. A major problem, among others, was General Thomas J. “Stonewall” Jackson’s corps, which was slow to move into place. Jackson was just back from his brilliant campaign in the Shenandoah Valley, but he showed none of his previous vigor and speed at Mechanicsville.

Lee planned to bring about 55,000 troops against Porter, but the mistakes made by Jackson and others meant there were only about 11,000. Lee lost 1,475 men; Union losses were only 361. But Lee had stunned McClellan, who then began to fall back away from Richmond. Lee continued to hammer on McClellan for the next week, and the Yankees retreated to the James River. McClellan did not threaten Richmond again, and he eventually sailed his army back to Washington, D.C.