There's a good novel, 'A Balcony in the Forest', centered on one of those reservists who were sent to defend the Ardennes route: a dreamy sort of man, who finds himself in command of a small fort and its men and develops a relationship with a local girl while wondering if the attack will really come. It was made into a movie, which is available on YouTube (only in French)

Also, the writer-aviator Antoine de St-Exupery served in a reconnaissance squadron in 1940 and wrote an outstanding book, 'Flight to Arras', which is partly personal narrative, partly a picture of the psychological atmosphere of the time, and partly a philosophical meditation. There's a review here:

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