This point made, Washington pushed on his preparations, or rather pushed on despite his lack of preparations, and on August 17, as has been said, wrote to De Grasse to meet him in the Chesapeake. He left the larger part of his own troops with Heath, to whom in carefully drawn instructions he intrusted the grave duty of guarding the Hudson and watching the British in New York. This done, he gathered his forces together, and on August 21 the army started on its march to the south. On the 23d and 24th it crossed the Hudson, without annoyance from the British of any kind. Washington had threatened New York so effectively, and manoeuvred so successfully, that Clinton could not be shaken in his belief that the real object of the Americans was his own army; and it was not until September 6 that he fully realized that his enemy was going to the south, and that Cornwallis was in danger. He even then hesitated and delayed, but finally dispatched Admiral Graves with the fleet to the Chesapeake. The Admiral came upon the French early on September 5, the very day that Washington was rejoicing in the news that De Grasse had arrived in the Chesapeake and had landed St. Simon and three thousand men to support Lafayette. As soon as the English fleet appeared, the French, although many of their men were on shore, sailed out and gave battle. An indecisive action ensued, in which the British suffered so much that five days later they burned one of their frigates and withdrew to New York. De Grasse returned to his anchorage, to find that De Barras had come in from Newport with eight ships and ten transports carrying ordnance.