Fair Oaks (Seven Pines)

On May 31, Confederate General Joseph E. Johnston attempted to overwhelm two Federal corps that appeared isolated south of the Chickahominy River. The Confederate assaults, although not well coordinated, succeeded in driving back the IV Corps and inflicting heavy casualties. Reinforcements arrived, and both sides fed more and more troops into the action. Supported by the III Corps and Maj. Gen. John Sedgwick's division of Maj. Gen. Edwin V. Sumner's II Corps (which crossed the rain-swollen river on Grapevine Bridge), the Federal position was finally stabilized. Gen. Johnston was seriously wounded during the action, and command of the Confederate army devolved temporarily to Maj. Gen. G.W. Smith. On June 1, the Confederates renewed their assaults against the Federals, who had brought up more reinforcements, but made little headway. Both sides claimed victory. Although the battle was tactically inconclusive, it was the largest battle in the Eastern Theater up to that time.

The most historically significant incident of the day occurred around dusk, when Johnston was struck in the right shoulder by a bullet, immediately followed by a shell fragment hitting him in the chest. He fell unconscious from his horse with a broken right shoulder blade and two broken ribs and was evacuated to Richmond. G.W. Smith assumed temporary command of the army. Smith, plagued with ill health, was indecisive about the next steps for the battle and made a bad impression on Confederate President Jefferson Davis and General Robert E. Lee, Davis's military adviser. After the end of fighting the following day, Davis replaced Smith with Lee as commander of the Army of Northern Virginia.

Also significant, the Army of the Potomac was accompanied by the Union Army Balloon Corps commanded by Prof. Thaddeus S. C. Lowe, who had established two balloon camps on the north side of the river, one at Gaines's Farm and one at Mechanicsville.