The regiment took part in Sir Samuel Auchmuty's disastrous expedition to the River Plate in October 1806, including the occupation of Montevideo in February 1807 during the Anglo-Spanish War. It then took part in the equally unsuccessfully Walcheren Campaign in autumn 1809: a total of 152 men from the regiment died of fever during that campaign. The regiment then embarked for Portugal and fought at the Battle of Arroyo dos Molinos, capturing General De Brune of the French Army, in October 1811 during the Peninsular War. It was also part of the covering force for the Siege of Badajoz in March 1812. In April 1813, the regiment returned to England. They were re-designated as a lancer formation in 1816 and became the 9th (or Queen's Royal) Lancers in honour of Queen Adelaide in 1830.