In 1794 after serving in the Army of the Coasts of Brest, Humbert served under Hoche in the Army of the Rhin-et-Moselle. Charged to prepare for an expedition against Ireland, he took command of the Légion des Francs under Hoche, sailing in the ill-fated Expédition d'Irlande against Bantry Bay in 1796, and was engaged in actions at sea against the Royal Navy. Contrary weather and enemy action forced this expedition to withdraw, on his return to France he served in the Army of the Sambre-et-Meuse, before being appointed to command the troops in another attempt to support a rising in Ireland in 1798. His command chiefly consisted of infantry of the 70th demi-brigade with a few artillerymen and some cavalry of the 3rd Hussars, however by the time he arrived off the Irish coast the United Irish