Timothy O'Sullivan (1840-1882) was a prolific and accomplished photographer of the Civil War. In 1862, he photographed the coastal battles in South Carolina and Georgia, the first successful chronicler of a military campaign. For a time he worked for Brady, and O'Sullivan also took photographs at Chancellorsville, Gettysburg, and Spotsylvania.
"93rd New York Infantry at Antietam: Union troops gather near Sharpsburg, Maryland, on September 16, 1862, the day before the Battle of Antietam, which would become the bloodiest single day in American history. (Photo Credit: Library of Congress )."