mandelbug definition: Noun (plural mandelbugs) 1. (computing) A software bug whose behaviour appears to be chaotic. ...
The bloodiest single day of battle was Antietam (26,134 casualties). The bloodiest battle, however - which lasted three days - was Gettysburg (51,112 casualties). July 21, 1861.
The bloodiest one day battle in American History is the Battle of  Antietam (Sharpsburg), Maryland, fought September 17th, 1862,  during the American Civil War.