As the 1st battalion left, the 2nd battalion was dispatched from Ireland to Spain for service in the Peninsular War. The 2nd battalion fought at the Battle of Bussaco in September 1810 before falling back to the Lines of Torres Vedras. The 2nd battalion fought with great distinction at the Battle of Fuentes de Oñoro in May 1811, the siege of Ciudad Rodrigo in January 1812 and the bloody siege of Badajoz in March 1812 before returning home to recruit. The 1st battalion returned to the Peninsula in time to fight in the Battle of Salamanca in July 1812, the siege of Burgos in September 1812 and the Battle of Vitoria in June 1813. It then pursued the French Army into France and fought at the Battle of the Pyrenees in July 1813, the Battle of Nivelle in November 1813 and the Battle of the Nive in December 1813 before seeing action at the Battle of Orthez in February 1814 and the Battle of Toulouse in April 1814.