casualty figures for the second day of gettysburg are difficult to assess because both armies reported by unit after the full battle, not by day. one estimate is that the confederates lost approximately 6,000 killed, missing, or wounded from hood's, mclaws's, and anderson's divisions, amounting to 30–40% casualties. union casualties in these actions probably exceeded 9,000. an estimate for the day's total (including the culp's and cemetery hill actions) by historian noah trudeau is 10,000 union, 6,800 confederate. this is in comparison to approximately 9,000 union and 6,000 confederate casualties on the first day, although there were much larger percentages of the armies engaged the second. some estimates of total casualties for the day run as high as 20,000 and declare it the bloodiest day of the battle of gettysburg. it is a testament to the ferocity of the day's battle that such high casualties figures resulted even with much of the fighting not occurring until late in the afternoon and thereafter lasting about six hours. by comparison, the battle of antietam—known famously as the bloodiest single day in american military history with nearly 23,000 casualties—was an engagement that lasted twelve hours, or about twice as long.