[1] He joined the Navy in 1780,[1] at the age of 14 as a novice on the coast guard cutter Pilote-des-Indes, cruising the English Channel, and on which he distinguished himself during the capture of a British privateer off Chausey.

[3] In February 1793, when war broke out against England, L'Hermite was first officer on the frigate Résolue, and he engaged in commerce raiding in the Channel and off the Atlantic coast of France.

Promoted to lieutenant in August 1793, he received command of the Tamise, recently captured from the British by the frigate division to which Résolue belonged.

[1] After extensive tests, Tamise conducted two patrols in the Channel, capturing over 60 prizes,[1] and was then attached to Montagne, the flagship of the Brest squadron.

[4][note 2] L'Hermitte then led the frigates Seine and Galathée and a corvette to Christiansand, visiting several harbours of the coast of Norway to capture British merchantmen that had fled there.

From February 1796, L'Hermite captained the frigate Vertu in a squadron led by Admiral Sercey, bound for île de France.

[5] When they arrived at Surabaya, the crew of Preneuse mutinied when L'Hermite decided to send the captured flags to Admiral Sercey.

[5] On 4 September 1799, Preneuse engaged a British frigate squadron that she had approached in the fog and mistaken for merchant vessels, escaping after a furious fight that cost her 40 men.

[5] After a 22-hour chase, L'Hermite engaged Jupiter and managed to manoeuver into a favourable position from which he sent her a raking broadside at pistol range, forcing her to sail back to Cape Town[5] to avoid boarding.

[6] The squadron departed Lorient on 31 October 1805 and cruised off the Azores, Cape Verde, the coast of Africa up to Benin, crossed the Atlantic to Brazil, and sailed towards the Caribbean.

[6] Having captured around 50 ships and 10 million franc worth of goods during his 11-month campaign, L'Hermite was promoted to rear admiral and made a Baron of the Empire.

[2] Langlois de Sézanne painted two portraits, representing L'Hermite and his wife, which the family gave to the museum of Coutances.