Defence minister
In 1951, he was sent to French Indochina, where he was tasked to protect a railroad to Saigon and secure the sector of Bien Hoa. Promoted to Lieutenant Colonel, Lacheroy was transferred to Paris and made director of the Centre d'études asiatiques et africaines (CEAA). There, he developed a theory of Counter-insurgency warfare, by then known as "psychological action". In 1954, he served as adviser to Defence minister Maurice Bourgès-Maunoury, and Defence minister André Morice in 1956.