Son of a French family coming from Forez and Lyon (de Boissieu), Alain de Boissieu was a pupil at École Spéciale Militaire de Saint-Cyr (French military academy) in 1936 and Saumur (French cavalry school) in 1938. He was a cavalry officer during World War II and, with horses and sabre, made a successful charge (one of the last in cavalry history) against German troops on June 11, 1940.
A prisoner of the Germans, he managed to escape to Russia in March 1941. But Stalin was, at this time, the ally of Hitler. So he was sent for a while to a Russian camp. Finally, after Germany attacked Russia mid-1941, he joined general Charles de Gaulle and the Free French forces (FFL) in London.