Arthur Doublon a mechanic nicknamed Chignole by his army buddies is soon to become an aviator. He is betrothed to Sophie Bassinet whose dad is a coachman and mom is a janitor in Montmartre. On their way to Nancy, Chignole and his lieutenant, Old Charles, meet an American soldier from the Lafayette Escadrille. Soon afterwards, Chignole's dog, Boudoubadabou, is wounded by a shell burst and Racine, their mechanics, is killed by an enemy plane. Chignole jumps into his own plane and shoots the enemy. He gets a medal for his act of bravery but is moved to the infantry as a discipline measure.

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