This is a Hollywood (English language) movie from the 1940s, but it may have a French director and partially French cast in America for the war. It is about a French soldier during and immediately after the Fall of France (1941); he may have been a tank driver. At the start of the movie all he can think about is deserting the cause of France but the patriotism and death of those around him eventually changes his mind.

Near the start he is picked up by a truck carrying French soldiers from all over the front, but after being strafed the majority are killed.

He successfully winds up in a ship and I believe the end of the movie sees him joining the Free French.