A second battalion was raised in Perth in August 1804. The 1st Battalion embarked for Hanover in December 1805 and, after service in Germany, returned to England in February 1806. The battalion embarked for Portugal in June 1808 for service in the Peninsular War. It took part in the Battle of Roliça in August 1808 and the Battle of Vimeiro later that month before fighting under Lieutenant-General Sir John Moore at the Battle of Corunna in January 1809 and then taking part in the subsequent evacuation from the Peninsula. The regiment lost its territorial designation being renamed the 91st Regiment of Foot in April 1809. The 1st Battalion then took part in the disastrous Walcheren Campaign in autumn 1809.