General Washington, although he was notified promptly of the fleet's departure, was unaware of its destination. He heard on August 10 that the fleet appeared to be moving south of Philadelphia, possibly heading for Charleston, South Carolina. As a result, he prepared to move north to assist General Horatio Gates defend the Hudson River against Lieutenant General John Burgoyne's march south from Quebec. On August 21 he was alerted that the fleet had been spotted one week earlier at the mouth of Chesapeake Bay. Realizing the danger to Philadelphia, he immediately issued orders to move the entire army south with all speed. His orders to Major General John Sullivan, who commanded the front line defenses in eastern New Jersey, were to rejoin the main army "with all convenient speed".