Factual error: The bird hovering near Manech's lighthouse is supposed to be an Albatross, but it's a Gannet.
Other mistake: The opening scene shows a soldier lighting his cigarette from a lantern. Not only does the cigarette not touch the flame, no smoke is seen as the soldier puffs on it.
Factual error: In the beginning of the movie they state that it is January 1917, a short while later during the assault a Renault FT tank is shown taking part in the attack. The Renault FT tank did not see combat for the first time until the end of May 1918, over a year later.