She screened French cruisers several times as they unsuccessfully hunted for Italian ships after Italy declared war in June.

The turbines were designed to produce 74,000 metric horsepower (54,000 kW; 73,000 shp), which was intended to give the ships a maximum speed of 37 knots (69 km/h; 43 mph).

During L'Indomptable's sea trials on 26 July 1935, her turbines provided 96,112 metric horsepower (70,690 kW; 94,797 shp) and she reached 42.3 knots (78.3 km/h; 48.7 mph) for a single hour.

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

In 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 scheduled for the following year.

[9] 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.

[10] In anticipation of an Italian declaration of war, the Force de Raid, including the 8th Scout Division, assembled in Mers-el-Kébir, French Algeria, on 5–9 April, only to return to Brest when the Germans invaded Norway on the 10th.

On the night of 23/24 April 1940, the 8th Scout Division made a high-speed patrol of the Skaggerak, hoping to attack German merchantmen headed for Norway.

They encountered two patrol boats and damaged one of them while also engaging a pair of S-boats to little effect and narrowly missed spotting a convoy of minelayers.

[11] When the Forces de haute mer was formed on 25 September, L'Indomptable was the only ship of her class assigned to it and was one of its escorts when they made a training sortie into the Western Mediterranean on 16–18 October.

The Germans considered salvaging her and redesignated her as SG9, but the ship was badly damaged during Allied bombing raids on 4 February, 7 March and 29 April 1944 and she was deemed a constructive total loss.