On the march to Harrison's Landing on the James River, he reconnoitered and selected positions for the Battle of Gaines Mill, the passage of White Oak Swamp and the Battle of Malvern Hill. After the conclusion of his work in that campaign, he again was engaged in working on the defenses of Washington as chief engineer of the Department of Washington until May 1864. He had certain additional special assignments such as devising the defenses of Pittsburgh, Pennsylvania, during this period.
As he led his troops towards Harrison's Landing on the James River, he carefully selected positions for the Battle of Gaines Mill, the passage through White Oak Swamp, and the Battle of Malvern Hill. Following the completion of his work in that campaign, he was again responsible for overseeing the defenses of Washington as chief engineer of the Department of Washington until May 1864. He also had specific additional duties such as designing the defenses of Pittsburgh, Pennsylvania.