In June 1864, Confederate Gen. Robert E. Lee detached Gen. Jubal A. Early's corps from the Richmond battlefields and sent it to the Shenandoah Valley to counter Union Gen. David Hunter's army. After driving Hunter into West Virginia, Early invaded Maryland toward Washington, D.C., to draw Union troops from Richmond and free Confederate prisoners at Point Lookout. On July 9, Early sent Gen. Bradley T. Johnson's cavalry brigade, including Maj. Harry Gilmor and his cavalry, eastward toward Baltimore, while Union Gen. Lew Wallace delayed Early at the Battle of Monocacy as Federal reinforcements strengthened the capital's defenses. Early briefly probed those defenses on July 11-12 and then withdrew to the Shenandoah Valley, where he halted the Federal pursuit at Cool Spring on July 17-18. Although he failed to take Washington, the invasion diverted Federal resources. Early on the evening of July 17, 1864, Confederate forces under Gens. Gabriel C. Wharton and Robert E. Rodes counterattacked Union Col. Joseph Thoburn's division across the Shenandoah River. While Rodes's men pressed Thornton's right flank, Wharton staged two attacks that drove the Federals back toward the river, but Union artillery on high ground stopped the Confederate advance. An artillery duel lasted into the evening as Union forces withdrew across the river under cover of darkness, and by 9 P.M. the Battle of Cool Spring was over. Wharton and Rodes were both native Virginians who studied civil engineering at Virginia Military Institute. Wharton graduated in 1847, became a mining engineer in the Arizona Territory, later returned to Virginia in May 1864, and after the war resumed engineering and served in the Virginia General Assembly until his death in Radford in 1906. Rodes graduated in 1848, taught at Virginia Military Institute until 1851, then worked as a railroad engineer in Alabama, joined the Confederate army there when the war began, fought in the east, and died at the Third Battle of Winchester on September 19, 1864.