The film shows General Terry arriving with his men to save the day. In reality, he arrived long after the battle was over.
"Major Benton" is obviously based on Major Frederick Benteen, but his actions in this film do not relate very directly to his historic basis. Benteen may have hated Custer, but was too professional a soldier to strike his commanding officer, no matter how much he wanted to.
During the Civil War, Marcus Reno was an officer in the Union army, not the Confederate army. Also, his only child was a son, not a daughter.
Neither Custer nor Reno had wagons with them during the final battles. The wagons were left behind so the column could travel faster.
The Arizona desert landscape is so utterly wrong for the sweeping grassy hills of the Little Big Horn battlefield, that it's inexcusable. If it were a battle few knew, that might be one thing. But this is like portraying the D-Day invasion of Normandy as an Arizona desert battle. Then, add to the unrealistic uniforms that, albeit popular in 1960s Westerns, did not reflect the US Army look of the Indian Wars in the 1870-80s.
In the scene just after a soldier tells a group of miners they have to leave, a Native warrior who has been watching them goes to get on his horse, which has a blanket over it to make it appear he is riding bareback, as Indians did. The Indian very obviously uses the stirrup on the hidden saddle to mount his horse.
The battle took place in June of 1876. The American flag seen at the end of the film has 38 stars representing 38 states. The 38th state, Colorado, was not admitted to the Union until August 1, 1876, more than a month after the battle.
Opening scene Darren McGavin used a 1873 Colt revolver with what appeared to be 10 inch barrel. The longest barrel Colt used was a 7.5 inch barrel.
The Little Bighorn battlefield was all wrong. The movie depicted a flat, desert terrain. In reality, Custer's last stand took place among steep, grassy hills overlooking a winding river.