La France (2007)

In France in the darkest days of the Great War Camille receives an alarming letter from her soldier boyfriend. Disguising herself as a man she sets off to try and find him. As she lives near the Western Fromt she hooks up with a passing group of French soldiers without too much trouble. But there's something a bit odd about these stragglers, and it's not just their habit of bursting into song at every opportunity.