Edit - Though some have compared Gettysburg to Waterloo and Gen. Alexander Webb later went so far as to term it the "Waterloo of the Rebellion," it has not been known as the "Waterloo of the Confederacy."
That would be the Battle of the Five Armies. Bilbo Baggins was dismayed to learn that the dwarves, elves, men and .... oh, wait sorry... no...
Battle of Five Forks! Yes., that's it.
This happened in 1865 when General Pickett found that he'd brought fish knives but not fish forks - he'd left them behind with his army which was about to face Sheridan armed only with the forks. Lost Cause mythology holds that had they been equipped with the knives, Sheridan could not have prevailed. Source: www.50 Shads of Grey.com