Factual error: When William Holden visits the Special Operations HQ for the first time a black vehicle is seen pulling in to the complex. The car is a 1948 Dodge or other Chrysler product which had not yet been manufactured.
Factual error: In the last scene of the chess game, you can see that both the Knight and Death have castled. Castling was introduced to the game of chess in the 16th century, well after the film is set.
Factual error: In one scene where Travis walks out the door of the kitchen half of the cabin, there is a thermometer nailed beside the door. In the late 1860's, when the movie takes place, thermometers like that were not available.
Factual error: When the UBoat changes course, Andrews, operating the radar repeater, is immediately able to provide the bridge with the target's new course and speed. This would be impossible without extensive calculations and at least range and bearing plots once the target has steadied up on the new course, either figured on the scope screen or on a maneuvering board. One must remember that both vessels' courses and speeds must be taken into account when making computations, and the relative direction of a target's travel most often is not its true course.
Factual error: As the movie opens, the submarine is dispatching frogmen to acquire Japanese mines that are sonar-proof. The problem with this is that in order to locate mines by sonar, either the mines must make noises to be picked up by passive hydrophones, or the submarine has to start pinging with active sonar. Doing this makes the submarine vulnerable to any enemy listening in. I can't imagine a submarine venturing into a mined strait, announcing to one and all, "Here I am"..
Factual error: While flying across the U.S. before the Atlantic attempt Stewart lands and exits the plane. While doing a quick inspection of the airframe he approaches the engine and puts his hand on one of the radial engines cylinders which would have still been several hundred degrees, so should have resulted in a serious burn.
Factual error: The train's locomotive has a steel cab, an electric headlight, and other modern applications. Overall, it more closely resembles an early 20th century steam engine than that of the 1880's, when the movie supposedly takes place.
Factual error: When Vince Edwards is marking months off the calendar he marks months off on two consecutive years that have the same days of the week. That never happens.
Factual error: Montana introduces himself as Sergeant First Class Montana, but his helmet and sleeve insignia shows the rank of Staff Sergeant.
Factual error: Sgt. Brennan and the Base Commander are riding in a staff car. They get out to see new runway construction, and when they get back in the car, Sgt. Brennan gets in first, followed by the Base Commander. Sgt. Brennan is on the right in the rear seat. According to proper protocol, the junior person sits to the left of the senior person. He should have been to the left of the CO.
Factual error: They stopped off at a European port after at least a few days after leaving, presumably, Southampton UK. Perhaps they embarked in Holland or Germany but that voyage to a French port would not have taken days on the open sea.