The Pennsylvania Reserves exhausted and the fierceness of Gaines' Mill

At the Battle of Mechanicsville on June 26, the Pennsylvania Reserves, a Union infantry division commanded by General George McCall, had experienced their first encounter with close-quarters combat and were compelled to withdraw. They suffered a grueling day of Confederate attacks on June 27 at Gaines' Mill, and one of their best general officers, John Reynolds, was captured. The weary Pennsylvanians were now at Glendale, in the middle of the Union battle line, gazing into the thick forest to the west, where the Confederate army was hidden.

With a rebel scream, Longstreet's division emerged from the forest around 5:00 p.m. By driving in the left-most section of the Pennsylvanian skirmishers, capturing Captain Otto Diederichs' artillery, seizing the Whitlock farmhouse, and turning the Pennsylvanians' left flank, General James Kemper's Virginia brigade turned the battle. General Micah Jenkins' second Confederate brigade made a break for the six cannons of Captain James Cooper's battery in the middle of the Union line. One witness said there was "more actual bayonet, & butt of the gun, melee fighting than any other occasion I know of in the war" during the Pennsylvanians' hasty attempt to defend their firearms. The field was torn apart by fierce hand-to-hand combat before both sides withdrew, bloodied and worn out, into their respective wooded positions.