June 1862: Captain John T Tidball of the Union Army poses with his staff at Fair Oakes, Virginia, during the American Civil War. (Photo by J. F. Gibson/Hulton Archive/Getty Images)

1859: Two officers of the US Army on a road near the USMA (United States Military Academy) on the Hudson River at West Point, New York State. (Photo by William England/London Stereoscopic Company/Getty Images)

A group of Northern soldiers from the Army of the Potomac takes advantage of a respite from battle to write letters and mend clothing during the American Civil War, early 1860s. (Photo by Hulton Archive/Getty Images)

1861: American Union politicians and soldiers taking part in a council of war, (from left) Abraham Lincoln, William Henry Seward, Winfield Scott, Simon Cameron, George McClellan, Benjamin Butler, John Wool, Robert Anderson, John Fremont and John Dix. (Photo by Hulton Archive/Getty Images)

A dead Confederate soldier in Devil's Den, Gettysburg. Photograph entitled 'The Home of a Rebel Sharpshooter, Gettysburg', from 'Gardner's 'Photographic Sketchbook of the Civil War' Volume I, plate 41 - pub. 1866. (Photo by Alexander Gardner/Getty Images)

July 1863: The battlefield at Gettysburg in Pennsylvania, after the bloodiest battle of America's Civil war, in which nearly 6000 soldiers died in 3 days of fighting, from 1 July to 3 July 1863. (Photo by Hulton Archive/Getty Images)