When war was declared in September 1939, all of the Le Fantasques were assigned to the Force de Raid which was tasked to hunt down German commerce raiders and blockade runners.

Le Fantasque and two of her sister ships were based in Dakar, French West Africa, to patrol the Central Atlantic for several months in late 1939.

They returned to Metropolitan France before the end of the year and were transferred to French Algeria in late April 1940 in case Italy decided to enter the war.

During her sea trials on 11 July 1935, her turbines provided 96,773 metric horsepower (71,176 kW; 95,449 shp) and she reached 41.4 knots (76.7 km/h; 47.6 mph) for a single hour.

After the war began in September, 200 kg depth-charge stowage increased to 48 and a pair of rails were installed on the stern for 35-kilogram (77 lb) depth charges.

In May 1942 the ship was provided with an Alpha-2 sonar system in cases pending the modification of the hull to accommodate the required flexible underwater dome.

The 10th Scout Division, together with British ships, was assigned to Force X that was based in Dakar, French West Africa from 10 October to 18 November.

[8] During 21–30 October, the Force de Raid, including all of the Le Fantasques, screened Convoy KJ 4 against a possible attack by the heavy cruiser Admiral Graf Spee.

On 25 November, together with Le Terrible and the heavy cruiser Dupleix, she captured the 4,627-gross register ton (GRT) German merchantman SS Santa Fé.

[10] Le Fantasque took part in a sortie by the Force de Raid into the Western Mediterranean on 12–13 June, after Italy declared war on the Allies on the 10th.

In response, the Germans and Italians authorized the Vichy French to send ships to the Gulf of Guinea to bring the rebellious colonies back under control.

The destroyers lacked enough range to reach Dakar at the 24 knots (44 km/h; 28 mph) ordered by Contre amiral (Rear Admiral) Bourragué and were forced to return to Casablanca.

[13] The Vichy destroyers were tasked to make a continuous smoke screen to protect the cruisers as they maneuvered to avoid British shells; Le Fantasque was not damaged during the battle.

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.

The sisters were among the escorts for the British Force H during the Salerno landings (Operation Avalanche) on 9 September and helped to shoot down a German aircraft that night.

The following month, the sisters conducted two unsuccessful raids searching for German shipping in the Aegean Sea on 19–24 November in conjunction with the British light cruiser Neptune.

After the Allied victory during the Battle of the Bay of Biscay on the 28th, the sisters sailed to Gibraltar, but only stayed a few days before returning to the Azores to continue their search for blockade runners.

The ships were refitted and then transferred to Alexandria, Egypt, to conduct patrols south of Crete and in the Aegean in April where they had no engagements other than a bombardment of Kos.

During the last raid on the night of 24/25, Le Fantasque's port propeller shaft began vibrating which limited her to a speed of 25 knots (46 km/h; 29 mph).

On 15 August, the 10th LCD provided naval gunfire support during Operation Dragoon, the Allied landing in Provence, Le Fantasque firing 280 shells from her main guns.