This cannon is likely one that was used in the Confederate blockade of the Potomac River, which included four batteries dug into what is now Marine Corps Base Quantico. It overlooks the Potomac from the Waller Hill neighborhood, the site where one of the batteries was located during the winter of 1861 and 1862. - This cannon is likely one that was used in the Confederate blockade of the Potomac River, which included four batteries dug into what is now Marine Corps Base Quantico. It overlooks the Potomac from the Waller Hill neighborhood, the site where one of the batteries was located during the winter of 1861 and 1862.