The French Naval Staff was arguing among themselves whether to convert one of their fast but poorly-protected heavy cruisers into a light aircraft carrier. When spies told of an Italian conversion already underway, the dithering stopped and Duquesne was selected to begin conversion immediately. The result was a fast, poorly protected CV with a large air complement for her size. She carried American Vought Vindicator dive-bombers and French Caudron naval fighters.

When war broke out, Duquesne and her CA sister Tourville were hunting German commerce raiders in the Bay of Bengal. She put into Durban to re-supply when the anguish of the French collapse drove her into the Allied camp. She sailed into the South Atlantic to join up with two British light battlecruisers when word came that an Italian squadron of cruisers, accompanied by a carrier, had successfully slipped by Gibraltar and was loose in the Atlantic. The Allied squadron sought battle when an Italian snooper aircraft indicated their nearby presence. Three scouting Vindicators found the Italian CVL Sagittario with all her planes fueled, armed, on deck, and launching. The armor-piercing bombs carried by the scouts penetrated deeply but did little damage to the flight deck other than small entry holes. The launching continued unabated. Italian AA had set a Vindicator on fire, and wounded pilot Henri Gaulois, shouting "Remember the Strasbourg", earned immortal fame by crashing his burning plane into the parked aircraft, starting an inferno that doomed the CVL.

When the Japanese threatened Samoa and other French Pacific protectorates, Duquesne left French West Africa and sailed "around the Horn" to the Pacific. In a narrow passage of the Straits of Magellan a Japanese submarine lying in wait fired four torpedoes into the thin hull of Duquesne and tore it apart. A rescue craft summoned from Chile found few survivors in the icy waters.