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. He was then assigned to the 6th Dragoons until his release in October 1929. Thereafter, he worked in the family business, Louis Dreyfus & Cie., eventually becoming a partner. He was recalled in August 1939 and served as a lieutenant in the 2nd Dragoon Regiment. He served two rotations in
Luxembourg and
France before again being discharged after the French capitulation. 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. He was forced to flee France in December 1942 and arrived back in England in January 1943. In April 1943, he joined the
1st Free French Division in Africa and was promoted to captain serving as a liaison officer with the Scottish
51st Highland Division. In December 1943, he requested assignment to the
Bomber Group "Lorraine" where he served as a gunner. 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 was then assigned as a representative of the French Army assigned to the 137th Wing of the Royal Air Force. ==Post military career==