[2] Called to military service, he became a cadet in the Reserve Cavalry School at Saumur in October 1928 and was released in May 1929 with the rank of sub-lieutenant.
[2] In 1941, along with his friends, Emile Laffon, Jacques Bounin and Emmanuel d'Astier, he came into contact with and joined the French Resistance.
Having extensive military training, Louis-Dreyfus was assigned responsibility for coordinating the resistance groups in the south of France.
From July 1944 until May 1945, he flew 81 bombing missions on the Western Front in Belgium, the Netherlands, and Germany.
He received four citations for his "tireless work" and for exhibiting the "best professional qualities, military and moral."
He also was Vice President on the Board of Directors of the Société d'entraide des Compagnons de la Libération (Society for the Support for members of the French Resistance), was a member of the Conseil supérieur de la marine marchande (Supreme Council of Marine Merchants) and vice-president of the Comité central des armateurs de France (Central Committee of French shipowners).
[3] In 1929, he married American-born Dolores Neubauer,[3] the daughter of a Jewish Brazilian father and a Mexican mother.
Dolores obtained custody of children and while Pierre was fighting in World War II; she moved to the United States in 1940 and returned to France in 1945.