On 9 November 1804, Mahé was promoted to Commander and became first officer on "Bucentaure" in December 1804. On 23 February, he was given command of the frigate "Hermione", on which he took part in the capture of , the Battle of Cape Finisterre, in the Battle of Trafalgar and in Lamellerie's expedition. In late 1807, he took part in a division under Rear-Admiral Baudin, ferrying troops to Martinique, before decommissioning "Hermione" on 26 May 1808.