She participated in World War II, first on the side of the Allies from 1939 to June 1940, then in the navy of Vichy France until she was scuttled at Toulon in November 1942.

Henri Poincaré was part of a fairly homogeneous series of 31 deep-sea patrol submarines also called "1,500-tonners" because of their displacement.

Propelled on the surface by two diesel engines producing a combined 6,000 horsepower (4,474 kW), they had a maximum speed of 18.6 knots (34.4 km/h; 21.4 mph).

Also called “deep-cruising submarines”, their range on the surface was 10,000 nautical miles (19,000 km; 12,000 mi) at 10 knots (19 km/h; 12 mph).

[3] At the start of World War II in September 1939, Henri Poincaré was assigned to the 4th Submarine Division in the 1st Squadron, home-ported at Brest, France.

[2] In November[2] and December[6] 1939, Henri Poincaré and Pascal patrolled in the Atlantic Ocean south of the Azores in search of German U-boats and their supply ships.

[7] As of 1 January 1942, Henri Poincaré was assigned to the 5th Submarine Division at Casablanca in French Morocco along with Fresnel, Pascal, and their sister ship Actéon.

[2] Moored at Berth 9 at the Darse Nord du Mourillon with her diesel engines disassembled,[2] Henri Poincaré was not yet able get underway when Germany and Italy occupied the Free Zone (French: Zone libre) of Vichy France on 27 November 1942, and she was among the French vessels scuttled at Toulon to prevent their seizure by Germany when German forces entered Toulon that day.

[2][3] Renamed FR 118 in Italian service,[3] she got underway from Toulon under her own power bound for La Spezia, Italy, on 2 September 1943.