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 Triomphant 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.

Le Triomphant played a minor role in the Norwegian Campaign in late April and was under repair when the Germans invaded France in May.

Ordered again to return to the Mediterranean, Le Triomphant was badly damaged by a typhoon in the Indian Ocean and had to be sent to the United States for permanent repairs and modernization that lasted until mid-1945.

During her sea trials on 26 November 1935, her turbines provided 98,529 metric horsepower (72,468 kW; 97,181 shp) and she reached 43.1 knots (79.8 km/h; 49.6 mph) for a single hour.

The Americans installed SA early-warning, SF surface-search and a British Type 285 fire-control radar, removed her aft torpedo tubes to save weight and converted some boiler feedwater tanks to fuel oil to improve her range.

[7] Ordered on 22 May 1931 as part of the 1930 Naval Program, Le Triomphant was laid down on 28 August 1931 by Ateliers et Chantiers de France at their shipyard in Dunkerque.

[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.

[11] 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 1940, 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.

She was partially refitted with British equipment in September–October and recommissioned on 23 October, although the ship was not ready to go back to sea until November when she was assigned to the 11th Escort Group, based on the Firth of Clyde in western Scotland.

Le Triomphant had constant problems with her propulsion machinery and propeller shafts during this time, which were aggravated when she broke loose from her mooring in Greenock during a gale in February 1941 and collided with a cargo ship.

The ship received a major refit at HM Dockyard, Devonport in May–July to prepare her for service in the Pacific Ocean for which she departed on 31 July via the Panama Canal.

Le Triomphant transported Georges Thierry d'Argenlieu, the Free French High Commissioner for the Pacific during this voyage and reached Papeete harbor on 23 September.

While leaving Wellington, New Zealand, Le Triomphant was damaged by a violent and sudden gust of wind and was under repair in Sydney, Australia, on 8 December when the Japanese attacked Pearl Harbor.

Le Triomphant resumed escort missions after the installation was completed on 17 June and Captain (Capitaine de vaisseau) Paul Ortoli relieved Auboyneau in July.

[19] Le Triomphant departed Fremantle the following day to return to the Mediterranean, accompanied by the American oil tanker SS Cedar Mills.

[20] En route, Le Triomphant stopped at Algiers where she was inspected by General Charles de Gaulle, leader of the Free French, and the High Commissioner for the Navy, Louis Jacquinot.

The sisters participated in a naval review in Ha Long Bay on 24 March before Le Triomphant departed for France on 9 April where she arrived at Toulon on 16 May.