During the attack on the train by the Messerschmitts, the prisoners on top are shooting at the aircraft with MP40s, a weapon that fired pistol rounds. As such, the 9mm rounds wouldn't have the range to even reach the aircraft, let alone damage them. However, the prisoners would have tried to fend the aircraft off with whatever weapons they had.
As the Padre is typing the order to change the routing of the train, he is using an American-made Underwood typewriter. This was a common office model in the 1950s in the U.S., but definitely not in use by the Germans in WW II. The German military would have used a Siemag or Adler pre-war model.
The markings on the wings of the crashed P-38 in the opening scene of the movie are incorrect markings that weren't used in World War II, as they were not adopted until 1947 by the United States Air Force. US Airplanes in 1943 would have used the markings without the red stripes in the bars of the roundel insignia. The red stripes were not adopted until 1947.
As the Padre begins to type the change orders for the train to be re-routed, he says (in German) the date of 11 Sep 1941. The U.S. was not involved in the war until December 1941. The year should have been 1943.
In the train station where the Gestapo agents follow the characters back to the train, Von Klemment is able to open the window shade behind him just as the Gestapo men are passing by. The window faces out the right side of the train. In the next scene, the Gestapo men approach the train car from the left side of the train. They should have boarded the car from the right.
When the prisoners are getting off the train for the first time in Rome to get food and water, in one scene it shows the German commander's private train car already attached to the end of the train. However a few scenes later it shows a rail-yard worker helping to guide the passenger car into place and coupling it to the last boxcar of the train.
When Ryan is released from the sweat box he is unshaven and filthy in his flight suit and is still in the same shape at the court martial. However, when the camp is immediately strafed by the planes and they run, in the next scene he has showered, shaved and in his dress uniform. Did he take time to clean-up and change cloths before leading the men out? Also his uniform switches back and forth between his flight suit and dress uniform.
Colonel Ryan's uniforms are inconsistent throughout the movie. He is seen, at times, in a simple flight suit, and at times in all or part of a dress uniform. Whilst pilots typically wore full uniforms under their flight suits, this is not shown when Ryan is first seen, and he would not have had anything other than his flight suit to wear.
When the men are hiding in the ruins, Col.Ryan is walking around checking on the troops. As he walks towards the camera he is clearly smoking and holding the cigarette in his right hand. The camera then switches to a close up of his body and his hands and the cigarette is gone. In the next shot he is finishing the cigarette and tossing it on the ground.
When Ryan throws a potato masher grenade at the attacking Germans in the final shootout, its arc will leave it far short of the distance and well to the right of its target. However, the next cut shows the grenade falling well on target.
All of the German soldiers carrying MP38/40 sub-machine guns (including all of the guards on the train) were wearing the wrong ammo pouches. The MP38/40 fired 9mm pistol ammunition from a 32-round detachable box magazine. The soldiers were all wearing cartridge pouches designed to hold 5-round stripper clips of 7.92mm ammunition for a bolt-action Mauser rifle. This means none of the Germans carrying sub-machine guns had any ready ammunition available once they fired the 32 rounds in their only magazine. This is a common mistake in WWII TV shows and movies.
After Italy's surrender is announced, it is claimed that Battaglia is now a civilian, not an army officer. This is incorrect and the characters would have known his proper (and unchanged) status. Although it surrendered, Italy continued to be a country, with a proper government and military forces. Battaglia would have been an officer in a non-belligerent (but untrusted) military.
At the very beginning of the movie when Col. Ryan's P-38 airplane is flying over the city trailing smoke, the smoke is coming from the center fuselage, not one of the engines. The sound of an engine sputtering is clearly heard, but the smoke is not coming from an engine.
When preparing the replacement orders to direct the train, Ryan reads the name "Obergruppenfuhrer Wilhelm von Kleist" from a printed form. Later in the movie, at von Kleist's HQ, the same title appears on his office door. However, a subsequent shot of the form shows only the rank (Obergruppenfuhrer [sic]) and the last name (von Kleist) of the signatory. There would be no way for Ryan to know the officer's first name. There are a number of errors here. Firstly, Obergruppenfuhrer was an SS rank. Von Kleist was a Wehrmacht (army) officer and would never be referred to using an SS rank. His correct rank in 1943 was Generalfeldmarschall (field marshal). Secondly, Field Marshal von Kleist's first name was Paul, not Wilhelm. Thirdly, in 1943 von Kleist was the commander of Army Group A in the Caucasus (on the Russian front), not the general staff.
When Ryan arrives at the POW camp and sees the burial of the British commanding officer, the British regiment is in formation by companies and the right hand marker of each company is holding a guidon (small flag on a staff). As the remains pass each company the guidon in lowered in salute. In the British Army (unlike in the US Army) individual companies do not carry guidons on parade (the only flags in an infantry regiment are the "Queen's Colours" and the "Regimental Colours") and flags are not lowered in salute.
The British prisoner, on being asked by Ryan whether the train will move, refers to the 'Engineer'. Unless he is aware that Americans use this term for the driver (unlikely), he would refer to the Driver.
Even in the 1940s, it was common for trains carrying hazardous goods to avoid routes through heavily populated areas unless they were unloading or loading cargo. The POWs could have simply chosen a route used by freight trains and avoided major cities entirely while traveling up the Italian peninsula.
Luftwaffe pilots are supposed to be flying ME-109s, but in fact they are flying Messerschmitt ME-108 Taifuns. The Taifun was a liaison/training aircraft, not a fighter, but its resemblance to the ME-109 made it a reasonable stand-in for the film.
A German Soldier mentions in German that the train is going to "Oesterreich" (Austria). From 1938-1945 Austria was a part of Germany and while its official name during that period was "Ostmark" instead of "Oesterreich," many Austrians (and some Germans) continued to refer to the territory by its original name.
Why didn't everyone just get out of the train and run through the train tunnel since Switzerland was on the other side? They were going to take a foot bridge which was supposed to be shorter, but since it was destroyed, it seems running through the tunnel itself was the next best option.
Though the "Messerschmitts" attacking the train are clearly either Bf 108 Taifuns or the French postwar variant Nord 1000, and the distance shots show them as being four-seat aircraft, the close-ups on the pilots are glaringly of single-seat fighter cockpits, although the canopies are reasonably close to the Bf 109s the craft were meant to be.
In the prison camp, the Italian soldiers are carrying German MP-40 submachine guns and Mauser 98 rifles. In reality, they would have carried Beretta MAB 38 submachine guns and M91 Carcano rifles. The MAB 38 was the standard-issue Italian submachine gun of World War II. The M91 Carcano was the standard-issue Italian army battle rifle.
When Fincham hurls a grenade at the mouth of the tunnel, during the final shootout the ground is littered with dead German soldiers. As the rocks explode, one of the "dead" soldiers raises his arm to ward off flying debris.
After the uniforms of the POWs are burned, new clothes are issued to them. All prisoners appear to get the exact same uniform they had before, specifically, Maj Fincham has the same style shirt as before - wearing it with at least 2 buttons undone. Others around him are wearing different style shirts. Replacement uniforms would all have come from the same source, possibly even Great Britain.
When the Germans first catch up with the escaped POW's at the ruins, several groups of prisoners try to escape by running. One German soldier shoots and kills some of the escaping prisoners; some of the POW's fall even though the German is not aiming at them.
When the Germans are chasing the POW's from the ruins, one German guard cuts off a group of about 9 prisoners and fires a short burst of bullets, yet about 6 prisoners he was not even aiming at, dropped dead anyway.
When Ryan is inspecting the prisoner's escape supplies, he picks up and examines a bottle. The top of the label lists "Mepacrine", an anti-malarial drug. Looking through the bottle, you can see compressed powder tablets. However, if you read the detail in the label, it lists the contents as an aqueous suspension (i.e. - a liquid product). Beyond that, the contents of the bottle are described as being female hormones ("Estrogenic substances consisting mainly of Estrone"), which would be of limited use to male prisoners trying to escape, as the primary listed ingredient causes nausea and vomiting when given to men. It would seem likely that the prop department was having a laugh with this one, as the label is on screen for under two seconds and is not easily read beyond the large print name at the top, without being able to pause the film.
The goof items below may give away important plot points.
Just before Ryan kills Gabriella, the train stops to take on water with the engine entering a spur to the right. At the end of the scene, the train moves away along the main line, without ever reversing for the engine to switch tracks.
The German commander of the pursuing train notices that the escaping POWs have loosened the tracks behind them. He quickly orders the engineer to slam on the brakes and the train comes to a halt in about three seconds. Given the train's massive size and speed, it would take much longer to come to a stop.
While the premise of the film is heartwarming ( the POWs are escaping to neutral Switzerland and freedom) in reality Switzerland was "neutral" in only the barest of terms. While it interned stranded pilots who crashed on its soil and didn't allow the Nazis to deport Jews from its territory, it also assisted the Nazis financially and kept up diplomatic relations with the Third Reich until the last weeks of the war.
Had the prisoners reached Switzerland, it was just as likely that they would have been disarmed and returned to German custody, especially during the 1943 setting of the film when the outcome of the conflict was still in doubt.