At the start of World War II in September 1939, Actéon was assigned to the 3rd Submarine Division based at Toulon, France. Her sister ships , , and made up the rest of the division.Huan, p. 49. In December 1939, Actéon joined Fresnel and their sister ships and in searching the central Atlantic Ocean for the German supply ship .Picard, p. 38. At the beginning of February 1940, the 3rd Submarine Division transferred briefly to Casablanca in French Morocco to patrol off the Canary Islands, where the Allies believed that German cargo ships had taken refuge at the beginning of the war and were serving as supply ships for German U-boats.
