In the beginning of the movie Rommel is being addressed as
'Field Marshal' 'though at that time he was still a General. He was promoted to Field Marshal after the capture of Tobruk, which occurred in 1942 not 1941, when the tide of war had swung back again in favor of the Germans.
The armored car used by Captain MacRoberts to destroy the German tank is a U.S. M-8. This vehicle did not enter service until 1943 in Europe. Appropriate British armored cars were in existence but were not readily available to Hollywood.
In the scene where "Tammy" and the others are being taken to a German pow camp in a truck convoy and strafed by allied aircraft, besides the inaccurate invasion stripes of the American P-51, other shots show stock footage of a Grumman Avenger diving in as well.
The Avenger was primarily used in the Pacific theater and did not enter service until June of '42.
When the British aircraft are attacking German trucks carrying
the prisoners, the planes shown in the distant shot are not the same planes as in the closeup. The planes in the closeup shot have black and white stripes painted on their wings, at the root and parallel to the fuselage. Such stripes were not used for identification until D-Day (they were called "invasion stripes" at the time) and then only in Europe.
When MacRoberts' wound is being treated, it appears high up on the left arm, near the shoulder. Two scenes later, the bandage is lower down on the bicep and the wound that would have been exposed is nowhere to be seen.
During the raid on the German camp there is a sign on a building reading "Hauptquartiers". Although the English word "Headquarters" might suggest a plural s, in German there doesn't exist such a form. The correct word would be "Hauptquartier" and the plural "Hauptquartiere"
When the captured MacRoberts requests a doctor the German soldiers calls for the "Oberarzt". An "Oberarzt" only can be found in civilian hospitals. The military rank would be "Oberstarzt" referring to a military surgeon in the rank of a Colonel. Otherwise he could have meant "Oberstabsarzt" which would have been a Major then.
During the last few scenes in the dugout, the characters all appear in various states of dirty, dusty, and disheveled, but the radio telephone, papers, and lanterns are all perfectly clean and orderly.
During the German tank/infantry attack mid-way into the film, a German throws himself on the barb-wire. When you see him getting up, he throws his rifle with a bayonet backwards, and you see the weapon is just rubber as it wobbles uncontrollably.