The movie is set in the around 1879-1880, 15 years after General Sheridan's campaign through the Shenandoah Valley. One of the songs in the movie, "Down by the Glenside (The Bold Fenian Men)," however, was not written until 1916.
When the regimental singers are serenading Kathleen Yorke and General Sheridan outside Colonel Yorke's tent there are several lanterns hanging from the top of the opening. The lantern on the right side of the tent post clearly has an electric light bulb in it.
The guitars in the film were far from authentic. One instrument in particular stands out: a classic pre-war Martin D-45 (manufactured between 1933 and 1942), which, by the number of frets, appears to be from 1937 or 1938. Played in this film by Bob Nolan of the Sons of the Pioneers, the D-45 is lavishly inlaid with abalone shell on all edges, front and back, plus around the soundhole. When new, it sold for a price fifty percent higher than a brand new car. As such, it would have been far out of reach for a lowly enlisted cavalryman, even if they had been available in the 1870's. The current new street price is a much more "reasonable" $8,659.00. A pre-war D-45 can sell for $250,000.
On the covered wagon carrying Kathleen Yorke during the Indian attack, when the driver falls off, the canvas behind Mrs Yorke is wide open. Later, when another trooper jumps on to drive the wagon, the canvas is closed tightly.
After the wagon train is rescued, Sandy Boone remains behind with Mrs. Yorke as the command rides off in pursuit of the captured children. Later, he is present with the troops to be picked by Tyree to sneak into the Mexican village.
When Travis meets up with Sandy and Jeff as they escort the children, he jumps off his horse and sits on the ground just in front of it. After Sandy gives him a can of beans Travis is sitting to the side of the horse, then to the front of it, then to the side of it. It looks like half the scene was filmed in a studio with Travis beside the horse and half in the open with Travis in front of the horse.
As Col. Kirby and his troop approach the Rio Grande, we are shown a wide shot of the river in the distance with no sign of an engagement between the Apache and the Mexican soldiers.
As the troop gets closer, we see smoke rising and the Mexican soldiers start to approach the river bank.
When Quincannon is addressing the recruits about horsemanship, Sandy takes his hand out of his pocket and removes the hay straw from his mouth. When the camera angle changes to behind Sandy, he has his thumb looped through his suspenders and the straw is back in his mouth. When it changes to the front view of Sandy, his hand is back in his pocket.
When Col Kirby enters the Rio Grande to meet with the Mexican officer, he orders the bugler to sound flourishes. The shot from the US side as they enter the river has the bugler to Kirby's right. The camera angle changes to the Mexican side and the bugler is now to Kirby's left.
For most of the movie, the troopers are carrying trapdoor carbines, including the escort for the women and children. Of the three troopers who entered the church, Boone and Yorke had been a part of the escort however, Tyree escaped from the fort without any weapons. The rest of the troop and the skirmishers are now carrying Winchester rifles when they charge the village.
During the Indian attack on the wagon train, Kathleen Yorke is in the driver's seat of a wagon by herself. There is another person visible in the back of the wagon who has the reins and is driving the wagon.
When the Indian shoots Lt. Col. Yorke (John Wayne) with an arrow in the village, he is aiming at the Colonel from a window. The arrow clearly has no sharp tip on it at all; it's simply a rounded blunt end like a practice arrow.