Alexander was an army officer.
Two years junior to Whistler at West Point, he resigned from the army in 1861, and distinguished himself as a Confederate artillery officer. He commanded Lee's artillery at Gettysburg, and was wounded at Petersburg. His war memoirs are a classic.
Cullum Memorial Edition, Register of Graduates and former cadets, United States Militery Academy, West Point, 1980; Porter Alexander, Edward, Fighting for the Confederacy: The personal Recollections of General Edward Porter Alexander, Gary W. Gallagher (Ed.) reprint, University of North Carolina Press, 1998.