When France declared war against Austria on 20 April 1792, Vidocq participated in the battles of the First Coalition, including the Battle of Valmy in September 1792. On 1 November 1792, he was promoted to corporal of grenadiers, but during his promotion ceremony, he challenged a fellow non-commissioned officer to a duel. This sergeant major refused the duel, so Vidocq hit him. Striking a superior officer could have led to a death sentence, so he deserted and enlisted in the 11th Chasseurs, concealing his history. On 6 November 1792, he fought under General Dumouriez in the Battle of Jemappes.