The conversion work began on 20 December at Yokosuka Naval Arsenal, and was originally scheduled to be completed within three months; however, numerous problems and issues arose, and the conversion work was not completed until 30 November 1942. She gained the distinction of being the only major warship damaged in the Doolittle Raid on 18 April. She received one direct hit from a bomb on the bow, plus several small incendiary bomb hits, with seven casualties among her crew. As an aircraft carrier, the vessel was renamed "Ryūhō".