Clinton began to assemble a force an expedition to take Charleston, withdrawing the forces from Newport for the purpose. Clinton took personal command of this campaign, and the task force with 14,000 men sailed south from New York at the end of the year. By early 1780, Clinton had brought Charleston under siege. In May, working together with Admiral Arbuthnot, he forced the surrender of the city, with its garrison of 5,000, in a stunning and serious defeat for the rebel cause. Arbuthnot and Clinton did not work together well during the siege, and their feuding lasted into 1781, with disastrous results for the unity of the British high command. Clinton's relationship with Cornwallis also deteriorated further during the siege, improving slightly after the American surrender and Clinton's departure for New York.