Understanding that great exertions were making to improve the fortifications, and that the garrison was gaining strength, Sir Henry Clinton ordered General Patterson to join him with the troops which could be spared from Georgia, and directed Lieutenant Colonel Tarlton, after supplying the horses which had been lost during a very stormy voyage from New York, to cover his march through South Carolina. In one of the excursions of that active officer to disperse the militia who assembled to oppose the progress of Patterson through the country, his cavalry encountered Lieutenant Colonel Washington, who commanded the remnant of Baylor's regiment, and were driven back with some loss; but the want of infantry disabled Washington from pressing his advantage. In defending Charleston, the command of the harbour is of great importance. To preserve this advantage, congress had ordered four frigates to South Carolina, which, with the marine force belonging to the state, and two French vessels, were placed under the command of Commodore Whipple. General Washington was the more sanguine in the hope of defending the harbour, because it was understood that the bar was impassable by a ship of the line, and that even a large frigate could not be brought over it, without first taking out her guns, or careening her so much that the crew would be unable to work her. On sounding within the bar it was discovered that the water was too shallow for the frigates to act with any effect, and that, in making the attempt, they would be exposed to the fire of the batteries which the assailants had erected. Under these circumstances, the officers of the navy were unanimously of opinion that no successful opposition could be made at the bar, and that the fleet might act more advantageously in concert with the fort on Sullivan's Island. The intention of disputing the passage over the bar being abandoned, Commodore Whipple moored his squadron in a line with fort Moultrie, in a narrow passage between Sullivan's Island and the middle ground; and the British ships, without their guns, passed the bar, and anchored in five fathom hole. It being now thought impossible to prevent the fleet from passing fort Moultrie, and taking such stations in Cooper River as would enable them to rake the batteries on shore, and to close that communication between the town and country, the plan of defence was once more changed, and the armed vessels were carried into the mouth of Cooper River, and sunk in a line from the town to Shute's folly. This was the critical moment for evacuating the town. The loss of the harbour rendered the defence of the place, if not desperate, so improbable, that the hope to maintain it, could not have been rationally entertained by a person, who was not deceived by the expectation of aids much more considerable than were actually received. [Sidenote: Opinion of General Washington on the subject of defending Charleston.]