The Brunswicker Ducal Corps, (in German: Herzoglich Braunschweigisches Korps), commonly known as the Black Brunswickers in english and the Schwarze Schar in german.
In 1809 the Fifth Coalition against Napoleon was formed between the Austrian Empire and the United Kingdom. The dispossessed Frederick William, who had been a strenuous critic of French domination in Germany, seized this opportunity to seek Austrian help to raise an armed force. To finance this venture he mortgaged his principality in Oels. In its initial incarnation (dated to 25 July 1809), the 2300-strong 'free' corps consisted of two battalions of infantry, one Jäger battalion, a company of sharpshooters, and a mixed cavalry contingent including Hussars and Uhlans.
Despite a successful campaign with their Austrian allies, the defeat of the latter at the Battle of Wagram on 6 July 1809 led to the Armistice of Znaim on 12 July. Frederick William refused to accept this and led his "Schwarze Schar" into Germany, succeeding in briefly taking control of the city of Brunswick. Faced with superior Westphalian forces, the Brunswickers conducted a remarkable fighting retreat across Germany, twice holding off the pursuing armies at the Battle of Halberstadt and the Battle of Ölper; finally being evacuated by the Royal Navy from the mouth of the River Weser. Landing in England, the duke was welcomed by his cousin and brother-in-law, the Prince Regent (later King George IV) and the Black Brunswickers entered British service.
Most units of the corps wore black uniforms, leading to the "black" nicknames of the unit, though some light units
(such as sharpshooters and uhlans) wore green uniforms. The Brunswickers wore a silvered skull badge on their hats.
Their title originated from Duke Frederick William, who claimed the Duchy of Brunswick-Lüneburg, which the French had abolished in order to incorporate its lands
into the French satellite Kingdom of Westphalia. The Black Brunswickers earned themselves a fearsome reputation over the following decade,
taking part in several significant battles including the pre-Waterloo engagement at Quatre Bras on 16 June 1815, where the Duke lost his life.
However, recruiting, the replacement of casualties, and finance had always been problematic, and the corps was disbanded in the early 1820s.