In 1794, after serving in the Army of the Coasts of Brest, Humbert served under Lazare Hoche in the Army of the Rhine and Moselle. Charged to prepare for an expedition to Ireland, he took command of the "Légion Noire" under Hoche, sailing in the ill-fated "Expédition d'Irlande" to Bantry Bay in 1796, and was engaged in actions at sea against the Royal Navy. Contrary weather and engagements with the British forced this expedition to withdraw. The trip home resulted in the action of 13 January 1797 during which Humbert, onboard the "Droits de l'Homme", narrowly escaped death. As the ship was sunk, hundreds of men perished, but Humbert was among the last to escape.