When fighting off the last German attack, Maj. Whittlesey fires 10 shots from his Colt 1911. The 1911 only hold at a maximum 8 shots.
According to a subtitle, the artillery friendly fire incident takes place on October 4. Later, when the Germans offer a message to surrender, a subtitle reads "October 6." Immediately after Major Whittlesey rejects the surrender demand, he has a conversation with Captain McMurtry in which the captain says, "We lost over sixty men to our own fire today." The captain is off by two days.
Private Krotoshinsky mentions how he "took the test", became an American and volunteered for military service. The real Abraham Krotoshinsky immigrated to the U.S. in 1912, worked as a barber until the outbreak of war, and did not become a citizen until after the war. Additionally he was one of the soldiers in Co K, 307th Infantry, not a replacement for the 308th.
When the plane is ready to take off for reconnaissance, the engine is started electronically. At the time of the war, engines were started by spinning the propeller blades manually, rather than by an electric ignition.
(at around 1h 24 mins) The collar insignia shown with everyone's collars now open, have clutch back devices, during this period they only had screw on or pin back insignia.
Lt. Holderman uses what is commonly known as the Weaver stance to shoot his pistol. This is a two handed stance. At the time the military trained officers and NCOs to fire sideways and one handed.
Private Philip Cepaglia's name is misspelled as "Cepeglia".
All soldiers in the film who are wearing gas mask bags in the "Ready" position have the bags on backwards. During WWI gas mask bags were worn with the snaps against the chest, not facing outward.
When Private Yoder shoots the German sniper, he cycles his weapon but no spent casing ejects.
When entering the first skirmish with the Germans in the forest, Capt McMurtry is seen cocking his pistol. It is clearly visible there is no actual round loaded into the chamber. Therefore the gun was not loaded.
When they attack the machine gun nest in the woods a German soldier is stabbed in the neck (with the sound effect) with a gun that has no bayonet.
The boots worn in the movie have modern rubber soled treads. This may be seen several times throughout the movie, both on killed and prone soldiers.
Sgt. Gaedeke's sleeve insignia are of WWII vintage, not WWI. WWI sergeant stripes were made of khaki or olive drab colored cloth. The stripes in the film are embroidered navy blue on olive drab.
When they first come up to the mill one of the soldiers is seen carrying a Lee Enfield No4 rifle which was used in WW2 not WW1.
Kar98k and Lee Enfield No. 4 rifles can be seen with American soldiers, the former of which couldn't of been in the hands of American forces even if captured do to it being anachronistic, and the No. 4 is just anachronistic.
After admonishing the newly arrived Lt. Leak on his appearance, Maj. Whittlesey says "Oh, Lieutenant; Welcome to the 308th." It can be easily seen that Whittlesey has actually said, "Welcome to the 307th." (K Company / 307th was also cut-off, but managed to find and fall-in with the 308th.)
A cameraman can be seen on the right of the screen for a second when four troops are about to destroy the German machine guns on the hill, about 20 minutes after the beginning of the movie.
At 41:28, when 2 soldiers are charging after Capt. Holderman and his company arrive, a camera can clearly be made out on the left side of the screen.
Private Chinn is left behind at the phone outpost in the woods because the battalion did not have enough phone wire to reach the objective at the mill. However in one scene Major Whittlesey, while at the mill, attempts to contact him by phone but the line is cut. Since the battalion did not have enough wire to reach the mill, he should not have had the phone, it should have been with Chinn.
After Cepeglia dies, the camera cuts to a different soldier and then back to Cepeglia. Despite the fact that his character is dead, the actor clearly swallows.