...f the Potomac as they emerged from their perilous march across White Oak Swamp to hear the firing of the gunboats on the James. It told them the Confederates had not yet preempted the occupation of Malvern Hill , which General Fitz John Porter's Corps was holding. Before the battle opened McClellan went aboard the Galena to consult with Commodore John Rodgers about a suitable base on the James. The gunbo...