During the Napoleonic Wars, the regiment first fought in the Peninsular War at the battles of Vimeiro and Corunna. It then took part in the disastrous Walcheren Campaign before returning to the Peninsula to fight at the Battle of Fuentes de Oñoro, the second Siege of Ciudad Rodrigo, the Battle of Salamanca and the unsuccessful Siege of Burgos. By the winter of 1812, the regiment was so depleted by casualties and disease that four companies were amalgamated with the equally weakened 2nd Battalion, 53rd Foot, to form the 2nd Provisional Battalion. Six cadre companies returned home to re-form. As part of the 4th Division, the Provisional Battalion took part in the Wellington's triumph at the Battle of Vittoria on 21 June 1813, followed by the Siege of San Sebastián and, 1814, the battles of Orthes and Toulouse.