Factual error: John Wayne's squadron lands on Guadacanal as part of the "Cactus Air Force" in August 1942. However, they are flying F6F-3 Hellcats, which were not available, even to the Navy, until the middle of 1943. To top it off, they are painted in a late-war camouflage scheme with late-war markings.
Factual error: In the very beginning of the movie broadcasters around the world are commenting on the mysterious spaceship. To lend a bit of calm and normalcy one broadcaster notes that despite what is happening many people are enjoying the fine spring weather in the Capital, to this end picnics and the wonderful cherry blossoms are plainly depicted. Shortly afterward when Klatu leaves the hospital, he is seen examining the cleaner's tag on the suit he "borrowed". This is where he adopted the name Carpenter. Clearly printed at the top of this tag is the date 7/18 1951, not spring by at least a few months.
Factual error: In the scene where the German East African troops are shooting at Bogart and Hepburn, their rifles are Gewehr 88 "Commission Rifles'" with five-shot magazines. In actuality, the German East African troops, under the command of Colonel Paul Von Letow-Vorbeck, were equipped with the absolute dregs of the Kaiser's arsenal: Gewehr 71 single-shot rifles, and Gewehr 71/84 8-round tube magazine rifles whose magazines usually got fouled and had to be used as single-shot rifles anyway.
Factual error: All of the Lydia's lieutenants are wearing epauletes on their left shoulders.only lieutenant commanders were permitted to wear one on the left shoulder, while the right shoulder was reserved for captains of less than 3 years' seniority.
Factual error: Several union soldiers wading across the waist-deep river (and later climbing out of the river) are carrying the U.S. Springfield Rifle, Model 1903, which is a bolt-action, magazine-fed rifle (Note especially the soldier who climbs out of the river holding his rifle above his head.) instead of the historical accurate muzzle loading rifle. The Model 1903 was adopted by the US Army in 1903 and used in World Wars I and II, but not the American Civil War. For a picture of the Model 1903 Springfield Rifle, see: http://www.army.mil/cmh-pg/Museums/Showcase/Myer/Myer-4h.htm. (00:14:30)
Factual error: The Pretorian Guard was not as loyal to the end as shown in the movie. Actually, they were bribed into rebelling against Nero.
Factual error: When Mrs. Cratchit passes the shop after buying the goose, the sign says butcher, but in that era, you would buy a goose from a poulter, seafood from a fishmonger, and beef, etc. from a butcher.
Factual error: The Thunderfish is closing on the Japanese I-boat, at under 6000 yards, Duke orders flank speed. The hydrophone operator on the I-boat would have to be deaf not to pick up the noise of Thunderfish's propellers at flank speed. For those pundits who claim that their sonar might be down, hydrophones are a passive listening system.
Factual error: At the end the narrator talks of "the Honourable" Winston Churchill. He was actually the Right Honourable.
Factual error: When the messenger has given the photos and materials to the doctor, the data is given to 'DA' or differential analyzer (just like in earth vs the flying saucers). What is shown is a standard card sorter which does nothing but put cards in order. This machine then outputs its info to a standard plotter which can only produce x-y diagrams. It would be easier to do the verification calculations by hand using a slide rule and some graph paper.
Factual error: Sargent Nevins (Arthur Kennedy) is shown playing a pinball machine in the military rec room. When the camera turns to the play field of the machine, it is clear that this machine has flippers, and flipper buttons are visible on the side of the body. The movie takes place in 1943, but flippers didn't appear on pinball machines until 1947. (First machine to have flippers was Gottlieb's 'Humpty Dumpty.'. (00:37:30)
Factual error: When the Reindeer aircraft is on the ground at Gander, Jimmy Stewart pulls the landing gear handle, but only the left main gear folds up. All three landing gear (left, right, and nose) would have folded together.