In December 1779, Arbuthnot conveyed the troops of Sir Henry Clinton to Charleston, South Carolina, and cooperated with him in laying siege to that city. The surrender document signed by prominent citizens was addressed to him and Clinton. On 26 September 1780 he was promoted to Vice-Admiral of the White. On 13 March 1781, he fought the French Newport squadron, at the Battle of Cape Henry, before returning to England.