In April 1805, he was reinstated again as commander of the 600 men of the expedition of Rear-Admiral Charles René Magon de Médine in Martinique, but never disembarked and returned to France. Protected by Antoine Charles Louis de Lasalle, who found Fournier a good alter ego ready for any and all escapades, he became the commander of his staff and distinguished himself in 1807 in cavalry charges at the battles of Eylau, Guttstadt and Friedland.