Harris was soon moving again, sailing to Portugal to participate in the opening actions of the British involvement in the Peninsular War. Harris was at the very first action, a skirmish at the town of Óbidos, where he saw Lieutenant Ralph Bunbury fall, the first British casualty of the war. On 17 August 1808 he was in the hotly contested skirmish line at Battle of Rolica, and saw serious opposition for the first time, reporting it as an exhilarating and terrifying experience. Many of his companions were killed at this action and the ensuing Battle of Vimeiro, but Harris remained unhurt, continuing the march to Salamanca before becoming trapped in northern Spain with the rest of Sir John Moore's army. The Light Brigade of Robert Craufurd, which included the 2nd/95th, did not march with the rest of the army to Corunna but marched to Vigo. The sights and horrors of the march remained with him for decades to come, and he was lucky to escape, claiming to be the very last man collected from the beaches at Vigo, and embarking for England in a severely weakened state.