In 1809 during the War of the Fifth Coalition, Frederick William, Duke of Brunswick-Wolfenbüttel raised a force of volunteers to fight Napoleon Bonaparte, who had conquered the Duke's lands. The Brunswick corps was provided with black uniforms, giving rise to their nickname, the Black Brunswickers. Both hussar cavalry and infantry in the force wore a "Totenkopf" badge, either in mourning for the duke's father, Charles William Ferdinand, Duke of Brunswick-Wolfenbüttel, who had been killed at the Battle of Jena–Auerstedt in 1806, or according to some sources, as a sign of revenge against the French. After fighting their way through Germany, the Black Brunswickers entered British service and fought with them in the Peninsular War and at the Battle of Waterloo. The Brunswick corps was eventually incorporated into the Prussian Army in 1866.