When World War II began on 1 September 1939 with the German invasion of Poland, Orion was part of the 12th Submarine Division in the 2nd Submarine Squadron in the 6th Squadron at Oran in Algeria. France entered the war on the side of the Allies on 3 September 1939. In October 1939, Orion moved to Casablanca in French Morocco, from which she conducted patrols in the Atlantic Ocean off the Canary Islands. On 4 March 1940, Orion sustained a cracked cylinder in one of her diesel engines, forcing her to proceed to Cherbourg, France, for repairs which were not expected to be completed until 1 September 1940. At Cherbourg, her diesel engines were dismantled and her batteries were removed, .
