The entire Virginia Defense Lines in Northern Virginia (including the Mount Vernon to Harpers Ferry sector) were commanded by Brigadier-General Philip St. George Cocke, as evidenced by his letter to Major-General Robert E. Lee related to the Aquia Defenses:
Alexandria, Va., April 26, 1861
General Lee, Commander-in-Chief:
The two 8-inch Columbiads have arrived, and, there being four rifled cannon at Aquia, under Captain [Reuben Lindsay] Walker, I shall proceed first to remove or destroy the light boats and buoys on the Potomac, and, at the same time order General Ruggles to hold himself in readiness to support by sufficient detachment of his troops. I shall do the same from this point, to cover and protect any working party, under the direction of the engineer, at a certain point on the Potomac. I would be glad to have Lieutenant Lee, of the Engineers, or some other officer of the Engineers, assigned for immediate service, to direct the construction of the works of this enterprise.
Philip St. Geo. Cocke,
(OR, Series I, Volume 2, p 781)