Factual error: All the Germans in the movie are cartoon-cutout fanatics: the rescued pilot stabs to death his English teacher, the German stragglers try to kill the lone British soldier, rather than avoiding him In order to survive, as would have been more probable. By 1917, soldiers on both sides were tired of war, and not driven by some ideological fury (as Germans inculcated with Nazi ideology were in WW2). Pilots especially had a code of honour, on both sides, and treated their downed colleagues with respect. That is not to say the Germans (particularly the Prussians) weren't brutal in battle. Most were conscripts and - like their British counterparts - desperate for the war to end after three years of fierce fighting, and countless casualties.
Factual error: The strong current of the river the main character falls into carries him to a considerable waterfall. There is nor has there ever been a river of that kind in Flanders' Fields, let alone a waterfall. Anyone who has any insight into the geography of the region will tell you it is flat as can be. The largest body of water, the Yzer, gently meanders and flows into the Channel, even during really rainy times.
Factual error: At the hospital towards the end, the doctor tells someone to go to "triage." The hospital is British. The term triage is French and comes from the Napoleonic wars and was coined by two French/Belgian doctors. The French were using the term triage during WW1 with plenty of photos to back this up. There is no evidence that the British or even the USA were using the term until about 1960 when it is mentioned by a Baltimore based medical facility. I can find no mention of its use in either WW2 or the Korean War. It only after this time that its usage becomes more widely used in the English speaking world.Stormin
Factual error: The British medical station is above ground and too close to the front lines. It is well within range of German artillery. Normally, such large open-air stations would be miles behind the front lines. Smaller, underground aid stations would give first aid to the wounded. Then they would move to the larger medical stations.
Other mistake: When Schofield leaves the truck at Écoust due to the bridge being out, he's told that the nearest intact bridge is 6 miles. However, when he is later going down-river, an intact bridge can be seen in the background.