When the Regiment de Walsh disbanded in 1791 Blackwell became a captain in the "Hussards Braconniers," or Poacher Hussars, an irregular cavalry corps raised by Jean Landrieux 'who placed it at the disposal of the Jacobin committees that were then relentlessly pursuing the proscribed nobles as traitors to France.' This corps was raised to the official status of the Twenty-first Cavalry Regiment in 1793 and became part of the Army of the North commanded by Charles Francois Dumouriez. On 20 September they won a decisive victory over the Prussians in the Battle of Valmy. On the same day, the National Convention met for the first time in the Tuileries Palace and its first act was to abolish the monarchy. They also won a decisive victory over the Austrians in the Battle of Jemappes on 6 November, 'which placed the country at their mercy and made clear their intentions of carrying their revolution abroad.' During this campaign Joachim Murat, who afterwards became a Marshal of France and King of Naples, served as a lieutenant under Blackwell. Murat too, had been intended for the priesthood.