Other mistake: In the final scene when they are about to charge Fort Wagner, Mathew Broderick yells "forward march!" and takes his first step with his right foot when it should have been his left foot like the rest of the battalion.
Other mistake: During the Battle of Agincourt, the same shots of soldiers being killed are used several times. Most noticeably there is one poor French soldier who dies from an arrow in his back at least twice.