General Clinton in December 1780 despatched Brigadier General Benedict Arnold (who had changed sides the previous September) with 1,600 men to Virginia. Arnold's instructions were to destroy Continental Army supplies and storage depots in that state, which had largely avoided military conflict before 1780, and then to establish a base for future operations at Portsmouth. On the afternoon of 4 January, Arnold sailed up the James River and landed his force at Westover, Virginia. Moving rapidly with an overnight forced march, he raided Richmond, the state capital, the next day. After another day of raiding, he returned to his boats and sailed to Portsmouth, which he then proceeded to fortify. The land approaches to this base were guarded by Virginia militia under the command of Brigadier General Peter Muhlenberg, but these were inexperienced as well as relatively small in number, and could not prevent the movement of British troops by ship on the readily navigable rivers in the area. Arnold's arrival prompted General Washington to mobilize land and naval forces to challenge him. Washington sent the Marquis de Lafayette with a Continental Army detachment to Virginia in February, and asked the French admiral at Newport, Rhode Island, Charles René Dominique Sochet, Chevalier Destouches, to send a naval force with addition troops to support Lafayette. When a storm in late January caused damage to the Royal Navy fleet watching Newport, Destouches slipped a ship of the line and two frigates out of Newport while Lafayette marched south. When these arrived near Portsmouth, Arnold withdrew his ships, which were lighter vessels with shallow drafts, up the Elizabeth River, and the French fleet, with its deeper drafts, was unable to follow. The French returned to Newport, but the effort, and further urging by Washington, prompted Destouches to sally out of Newport on 8 March with his entire fleet, seven ships of the line and a recently captured frigate, with 1,200 French troops aboard. When Clinton and Admiral Marriot Arbuthnot learned of this two days later, they immediately mobilized supporting resources. Arbuthnot sailed with eight ships of the line that very day, and, in naval action on 16 March, successfully prevented Destouches from entering Chesapeake Bay. Arbuthnot's fleet was followed by transports carrying 2,000 British Army troops under the command of General William Phillips. When Phillips and his troops were landed at Portsmouth on 26 March, Phillips, with seniority over Arnold, took command of