 There he served as "Aide-de-Camp" to General Kléber, who both received head wounds at Alexandria caused by an incendiary-device, 13 March 1801.After Kléber's assassination he was appointed AdC to General Menou.De Faÿ was present at the Battle of Austerlitz and served in Germany under General Milhaud, commanding the 22nd Chasseurs-à-Cheval Regiment, part of Marshal Murat's Reserve Cavalry Corps; shortly afterwards, on 24 December 1805, he was appointed Brigadier-General.