This experience prompted the General Staff to order eight patrol trawlers from the Delaunay Belleville shipyard in La Rochelle on December 13, 1916.

[2] The ship was powered by a 450 hp triple-expansion reciprocating steam engine,[1] enabling La Tanche to sail at a speed of 9 knots.

[2] The ship entered active service for the French Navy on December 10, 1918,[3] and on January 22, 1919 it was placed in reserve with the Loire zone flotilla in Group B, based at Lorient.

On the 25th of the same month, it was assigned to the Syrian flotilla, but on February 14, 1919 a counter-order reassigned it to Rochefort to join the Bay of Biscay patrol division, where it remained until September 25 of the same year.

[2] At the end of 1919, La Tanche was one of a group of 71 patrol boats the navy was seeking to dispose of after the war, and was sent to Marseille for decommissioning.

[2] La Tanche was purchased by the Secretary of the Merchant Navy to be transferred to the Office Scientifique et Technique des Pêches Maritimes.

[4] It was under the command of Raymond Rallier du Baty, then two officers from the fleet's crews, and was equipped with nansen bottles with thermometers and several sampling dredges capable of operating at depths of over 1,000 meters.

[4] However, the Office Scientifique et Technique des Pêches Maritimes ran into financial difficulties, despite assistance from the French Navy, and had to part company with La Tanche.

[8] On June 18, the Maritime prefect ordered all fishing boats to evacuate Lorient, and many civilians and soldiers fled the German advance.

[8] The 70 tons of coal needed to run the boats were loaded by hand, as the port's crane operators had left town the day before.

[8][n 2] Around 3 pm, La Tanche set sail with around 250 people on board, including apprentices from the French Navy's mechanics school.

[10] At 4:10 pm, just outside the harbor, in the Courreaux de Groix, the ship jumped on one of the magnetic mines dropped by a German plane near the rocks called "Les Errants" and "La Truie", and sank in a few minutes.