Cogny enlisted in the French Army before the outbreak of World War II, graduating in 1929 from the Fontainebleau artillery school, and was a battery commander by the time the war started. He was awarded the Croix de Guerre during early engagements.
Before the start of World War II, Cogny joined the French Army and graduated from the Fontainebleau artillery school in 1929. By the time the conflict started, he had become a battery commander. He received the prestigious Croix de Guerre award during his initial military operations.