This movie is so innocent and funny! The main actors are really comedians of their time: simple, hilarious yet charismatic. No one and nothing here is to take seriously (as too many Hollywood or narcissist comedians and actors of today). The theme is dark and the french way of dealing with it is extremely delightful: laugh and gratitude instead of suffering and despair. Some French people learned from the stupid thing that is war and that it is a game of corrupt governments, so they try to live as fully as possible. Fortunately, most of French care about their country and didn't fall on treason of joining the dictatorship of Vichy Government, as an hilarious scene in the movie shows.
By my review, you'll already guess there's a lot of chilchés: french are simple, revolutionaries and fight enjoying life as the Germans just follow orders. But stereotypes are always based on some truth.
Of course, this whole description is about movie. A lot of good soldiers died in both parts, in vain, just for the vanity of their highest superior who always survive. May they rest in peace.