Revealing mistake: When the 54th Mass. marches past a liberated plantation some black children wave them on. One of them is wearing a digital wristwatch.
Factual error: In the assault on Fort Wagner, the regiment attacks the fort from the wrong side. In reality, the troops attacked from the south.
Continuity mistake: During the first battle in the woods, the Union Regiment levels their un-bayonetted weapons and fires a volley at the Confederates. About 3 seconds later, without the order having been given, they are in hand to hand combat with bayonets fixed.
Revealing mistake: Rubber bayonets quiver every time the Federal troops hit the sand for protection during the climactic assault on Fort Wagner. It sort of wrecks the mood.
Other mistake: In the scene where muskets are issued to the 54th Massachusetts, only Pvt. Jupiter Sharts is revealed to be a marksman worthy of training the other troops by virtue of having previously hunted squirrels. The camera then zooms to a closeup of Pvt. Sharts aiming down the barrel with the wrong eye closed.
Continuity mistake: Just before the final battle begins, the shots pan several times from Shaw, to the sea, and then to the fort. When the camera angle is looking at Shaw, the sky is bright blue. When it shifts to the ocean, the sky instantaneously becomes brownish tan, and then becomes a dismal gray behind the fort.
Visible crew/equipment: When Shaw gets shot, he falls down. When he falls, you can see the squib wire out of his boot.
Factual error: In the movie, the soldiers of the 54th Mass. were not issued their uniform until long after enlistment. However, according to many history books about 54th Mass., the soldiers of 54th Mass. were issued their uniform immediately after enlistment.
Factual error: In some of the scenes in the video during their time at Readville camp, they celebrate Christmas. In actuality, the first volunteers arrived at Readville in February of 1863, and Shaw died in July of 1863, along with most of the regiment, so there is no possibility of having a Christmas during that time.
Deliberate mistake: When Trip lies face-down in a medical tent after the lashing punishment, his shoe is removed to show Col. Shaw his wounded feet from not having decent shoes. But the shoe removed looks perfectly fine, no holes in the sole, etc. Yet Trip's foot is raw and extremely bloodied! (I can see having some blisters from no socks, but straw or cloth bits prevent that.) Why not treat his foot wounds first rather than placing the shoes back on, then show to Col. Shaw.
Factual error: In the scene where Elwes and Brodrick are talking about the colored regiment (~13:00), Elwes is holding a bottle of Dom Pérignon champagne. The first vintage of Dom Pérignon is dated 1921 and would not have been available during the Civil War.
Continuity mistake: In the scene where the 54th is on parade, Shaw commands "eyes right" and looks to his right and points his sword down to the right. Then the next shot is a brief shot of his parents and then when they return to Shaw, his sword is pointing up in the normal marching position. There was no audible command to stop saluting.
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.
Audio problem: In the scene where Matthew Broderick is addressing the potential members of the 54th on horseback (right after he accepts the position), the army band is playing, but the visuals don't match the music. While we hear drumrolls, we only see single hits on the snare drums by the actors. And at least one drummer is playing in mid-air.
Factual error: During the burial scene at the end of the movie, the corpses of the 54th soldiers are shown with only their shoes removed. In reality, the corpses of the 54th dead were stripped of all usable clothing, as the South was desparate for any uniform parts (source: "A Brave, Black Regiment" by Louis Emilio). At the very least, the corpses of the officers would have been picked clean by souvenir hunters.
Continuity mistake: When the men refuse to accept their pay, the Colonel tears his paycheck in half. It tears straight down the middle. There is a brief shot of the men, and the camera returns to the colonel. There is a piece of his check in his hand and the tear is now diagonally across the paper.
Factual error: During the training of the regiment, there is one scene where Colonel Shaw is shown practising his swordsmanship. A row of stakes has been placed in the ground and a watermelon tied to each one which he slices apart with his sword as he gallops past.The caption tells us that it is February 1863 in Massachusetts. There is no way you could get fresh watermelons in that state at that time of year in 1863.
Continuity mistake: As the 54th charge Fort Wagner across the beach there is a long range shot of the troops running from the left to the right of the screen. Watch Matthew Broderick. He is holding his large wide-brimmed hat, which he does not wear (or even carry) in previous and subsequent scenes!