After the Allies invaded French North Africa on 8 November, French West Africa and its fleet, including "Le Fantasque" and her sister "Le Terrible", joined the Allies on 24 November. The sisters steamed to Casablanca, French Morocco, where their light anti-aircraft guns were removed on 21 January 1943 and then to the Charlestown Navy Yard in Boston to be modernized. Arriving on 21 February, "Le Fantasque"s refit lasted until 25 June and included the addition of a British Type 128D ASDIC system, installation of SA early-warning and SF surface search radars, the removal of her aft torpedo tubes and the conversion of some boiler feedwater tanks to fuel oil to improve her range. Her AA armament now consisted of eight Bofors guns in a quadruple mount superfiring over the aft 138.6 mm guns, and two twin mounts forward of the aft funnel; eight Oerlikon guns were also added in single mounts, four on the sides of the bridge and the remaining guns on platforms on the aft superstructure. These changes added about to her displacement; during speed trials on 12 June, the ship reached . After the refit, she was reclassified as a light cruiser and the 10th Scout Division was redesignated as the 10th Light Cruiser Division (). Despite the modernization work in Boston, the ships' turbines were prone to frequent breakdowns during heavy use and required a lot of maintenance. To compensate, the French adopted a policy of keeping two of the three ships in the 10th Light Cruiser Division (LCD) operational at any one time while the third ship was repaired.