In the scene where the 54th Massachusetts has just marched past the Southern plantation, a group of slave children run out to wave at them. After being greeted by Undertaker, they wave. One of the slave children has a digital watch on his hand.
The corrupt character of Gen. Charles Garrison Harker portrayed in the film by Bob Gunton was not present in South Carolina at the time the 54th Massachusetts was there. He was part of the Army of the Cumberland's Tullahoma Campaign in Tennessee at the time and was only 25 at the time, unlike Gunton who was 44 at the time of his portrayal.
After Col. Shaw is notified of his promotion, he and Maj. Forbes are outside talking. Maj. Forbes is drinking champagne from a Dom Pérignon bottle. This champagne (made by Moët & Chandon) was first made in 1921 and released for sale in 1936.
When Rawlins is promoted to Sergeant-Major, he is handed the insignia sewn onto a blue cloth backing. While this is common with Civil War reenactors, the stripes of the era were individual stripes that had to be sewn on one-by-one.
In the scene where Shaw finally loses patience with the Quartermaster, he marches in and demands 600 pairs of shoes and 1200 pairs of socks. After the initial interchange, Matthew (Shaw) says "Do you really think you can keep (pause) 700 Union soldiers..." Patently Matthew had forgotten just how many pairs he needed and the slight pause indicates he had momentarily forgotten his lines.
When Shaw and Cabot are talking to General Harter about their transferring their men to combat command, Cabot has his hands on his lap when the camera faces him, but as the camera faces General Harter, Cabot's face is leaning on one hand.
When Trip is scuffling with the white soldier on the road. Sgt Major Rawlins walks up to break it up, his coat is unbuttoned with his undershirt clearly visible. When the scene cuts to his dialogue, his coat is buttoned all the way up.
When Rawlins is promoted to Sergeant-Major on the boats, he is called to front and center. As he does so, he salutes, with his palm facing forwards, to the officers. However, in the next shot, his palm is facing down to the ground.
When Shaw is seen riding on his horse, using his saber in practice cutting watermelons, it is before Christmas and watermelons would not have been available for practice. They come in the late spring and early summer.
During the final battle scene with the 54th forming up for the attack on Ft. Wagner on the beach, the ocean is to their left. This would mean that they were headed south instead of north. Fort Wagner was actually attacked from the south, therefore, the Atlantic Ocean should be on the right, not the left.
In the film, Shaw asks who will carry the colors if they should fall during the assault on Fort Wagner. In reality, it was General Strong who asked this question, and Shaw was the one who volunteered to carry them.
The film depicts the 54th Masachusetts Infantry Regiment training through the Christmas holidays of 1862 (after the September 1862 Battle of Antietam), but the real 54th Massachusetts did not organize until March 1863, just four months before attacking Fort Wagner in the climactic scene.
Shaw did not receive the request to be Colonel of the 54th while at a party in Boston, nor did he accept immediately. In fact, he refused the command at least twice, feeling himself unworthy. It was only after some convinving by his friend (and the man who would later marry Shaw's sister) Charles Russell Lowell, commander of the 2nd Massachusetts Cavalry, he would accept the command. Lowell's own command was unique in that 5 companies of Californians (known as the California Battalion) served in it.
The film depicts the 54th Massachusetts Volunteer Infantry training through the Christmas holidays of 1862 (after the September 1862 Battle of Antietam). But the real 54th Massachusetts did not organize until March 1863, and it was engaged in its first battle on James Island, South Carolina, on July 16, 1863, and then Fort Wagner (the final battle in the film) on July 18, 1863. The 54th went on to fight at Olustee, Florida (February 20, 1864); Honey Hill, South Carolina (November 30, 1864); and Boykin's Mill, South Carolina (April 18, 1865).
Flogging was banned in the Union Army in 1861. Pvt. Trip would not have been whipped, at least not by someone as by-the-book as Colonel Shaw; however, there were harsh punishments, such as being "spread eagled" on the spare wheel of an artillery limber, which often broke the man's back.
The manner in which Colonel Shaw dies in the movie is based on fact. His final words were "Forward, Fifty-fourth!" before he was shot several times in the chest. The film depicts him falling on the parapet; in fact, he made it to the top, and his body fell into the fort.
In the movie, it is claimed that "over half" of the regiment was lost during the assault on Fort Wagner. However, official records state that the 54th sustained 272 casualties, which is closer to 40%. Of these casualties, only 116 were fatalities, just under one fifth of the men to storm the fort. If the 156 soldiers that were captured are included, it would bring the total to "over half". In formal military terms, though, "casualties" include captured soldiers. In any event, by most standards, including those of the Civil War, these are heavy casualties and the regiment was widely viewed as having performed bravely indeed.
In the movie, Shaw is surprised when the men refuse pay that was reduced because they are a "colored" regiment (though he eventually joins them in their refusal). In reality, the refusal was his idea, and he encouraged them to do it.
Gov. Andrew wanted the 54th to be an elite unit and so did not accept runaway slaves. In fact, among the soldiers of the 54th there was a private who was a medical doctor and all, or nearly all, of the men could read and write.
The character of Col. Montgomery is portrayed as a greedy, cynical, and hypocritical racist who relishes his former days of being slaveholder. The real James Montgomery was a actually a fanatical abolitionist in the vein of John Brown (for whom he considered mounting a rescue mission). Montgomery's fanaticism did lead him to plunder and burn Darien, GA. Montgomery's motives were sincere (if immoral and brutal), and not cynically excused as portrayed in the movie.
In the opening scenes, when Shaw is seen marching beside his soldiers towards the Antietam battle, the rank insignia on his epaulets change from that of a captain (two bars) to that of a second lieutenant (no insignia within the epaulet borders) because it's a flashback.
When the 54th returns from the Battle of James Island, the melody to "The Bonnie Blue Flag" can be heard in the background. While "The Bonnie Blue Flag" is a patriotic Southern song, actually closer to a Confederate National Anthem than "Dixie", the melody was not exclusive to that song and there were other songs with the same melody, including a humorous song titled "The Arms of Abraham" lamenting the experiences of a draftee in the Union Army, and the melody was popular on both sides of the war.
After Sgt. Maj. John Rawlins talks to a group of children standing by a white fence, he walks away and you can briefly see a digital wrist watch on a child on the right side of the screen as they wave goodbye.
When Shaw is being buried, he is shown being thrown into a mass grave still in his uniform minus his boots and socks. But, according to Confederate General Johnson Hagood, Shaw's body was stripped and robbed before being thrown into the grave.