Factual error: When Roberts makes a deal with the Captain, he demands that the Captain grant liberty to both sections (i.e., the entire crew), leaving only Roberts and one enlisted man aboard as the deck watch. All U.S. Navy ships must have enough personnel aboard at all times to get the ship underway immediately, if necessary, which is why the crew is divided into watch sections.
Continuity mistake: Lady is put in her bed and the master leaves the kitchen but he goes back in and puts a newspaper on the floor and leaves again but Lady gets out of her bed so the master comes back once more and puts her back in her bed but the newspaper on the floor has vanished.
Continuity mistake: During the desert chase sequence, when our hero is run off the road by Ernest B. his missing arm is momentarily transposed when he steps from the jeep.
Factual error: The movie takes place around the time of WWI, definitely before 1923. In the carnival scene, the calliope is heard playing "Ain't She Sweet". This was the number one song ... in 1927.
Audio problem: When Willa Harper is lying in bed talking to Harry her mouth movements are out of sync with the dialogue.
Visible crew/equipment: In the very first scene when the camera pans in to the butcher shop, you can clearly see the shadow of the cameraman on the lift.
Other mistake: At the beginning of the movie at the police station and the next morning at breakfast, it at least appears to be established that Grandma lives with Jim and his parents. After all, they had just moved from another city and Grandma was there early in the morning at breakfast time. However that's the last we see of her. She is never mentioned again nor is she there after Jim comes home from school or at anytime after the trouble starts. It would be unusual for someone to sleep through all that went on; but no one ever says anything about "being quite or we might wake Grandma up." After that scene at breakfast, she is forgotten.
Continuity mistake: When the soldiers are ambushed by the Germans, they jump off and Jack Kelly is wounded in the arm, showing a torn shirt and bloody arm. Later when Audie Murphy is wounded and in the hospital Jack Kelly visits him. The only bandage on him is on his hand, which wasn't injured before.
Factual error: When Jimmy Stewart is almost down to the runway during the bad weather, the aircraft exterior shots show the type of cloud tops found only at high altitude, not low to the ground.
Continuity mistake: In the scene where Trevor Howard and José Ferrer are sharing what appears to be some port (about 50 minutes into the movie), the port decanter has a drip stopper in the long shot which disappears in the close-up shot of Leslie Howard and then re-appears in the following longer shot.
Factual error: The system devised to get the height right was, in the film, said to have been thought of by the 617 Sqn crews following a visit to the theater. In reality it was devised by the 'boffins' at Farnborough.
Suggested correction: See many previously posted 'mistakes' of this type and the standard correction: this is not a documentary and never pretended to be. It is a war drama and many facts were changed to fit the action.
Those correction are often made in fallacy. Dramas based on historical accounts have liberty to change small or inconsequential things, like adding a person that may have never existed, or change a relationship for dramatic purposes. Despite not being a documentary, unless it's a fantasy film, changes in historical facts are mistakes (for example, a drama can't have the Eiffel Tower in London just because it's not a documentary).
Suggested correction: This was the version given in Brickhill's book. The real story wasn't published till many years after the film was made.
Factual error: When Kitchener is shown inspecting Harry's old regiment, one group of African or Egyptian troops is shown to be wearing the Pattern 1914 Infantry Equipment, not made until 1914 at the earliest. Additionally, it has the 1918 modification to have two closing straps, so is over 20 years too late for the 1894 date at that point.
Revealing mistake: Several shots and whole scenes throughout this film are flipped horizontally in such a blatant fashion that even the name of the ship, "Sans Souci," appears as a mirror image.
Deliberate mistake: Glenn Ford strikes the window in the library door with his briefcase and it instantly shatters. In reality, a blow delivered by a briefcase to a plate glass window would have produced no more than a scratch or crack.
Other mistake: While all the business signs in downtown Osaka are properly in Japanese, the local newspaper, The Osaka Times, is printed entirely in English.