Admiral Grasse made a fairly slow passage from Saint-Domingue through the Bahama Channel, assisted there by the powerful northerly current. His fleet had successfully intercepted and captured every ship met with and so preserved secrecy. A particularly satisfying capture was the British packet Queen Charlotte, for on board was Colonel Lord Rawdon, on his way home on sick leave from South Carolina. The result was that no news of the fleet's progress had gone ahead, though it was, of course, widely anticipated. Certainly Cornwallis's frantic note to Clinton on 31 August is a good indication of his surprise.

Like Commodore Destouches in March, Admiral Grasse's purpose was to occupy Chesapeake Bay, and so deny it to the Royal Navy. This would permit the American and French land forces to be reinforced and assisted in their action against Cornwallis. But Grasse did not know before he set out where Cornwallis was, or that he had begun (only three days before Grasse sailed) to fortify his position at Yorktown. He may have discovered this from one or other of the ships he captured on the voyage north, but one cannot be sure. But when he arrived, he was immediately contacted by Brigadier-General Portail, Washington's engineer aide, who had been with La Fayette for some days, and Portail had been sent south with the express purpose of explaining to Grasse what Washington and Rochambeau intended.

Grasse was in a hurry. He did not know anything of the British fleet, either its strength or its position, but he could certainly expect to find it coming at him at any moment. Portail, with two colonels from La Fayette's force, contacted Grasse as soon as the ships were sighted, and put St-Simon in contact with La Fayette, who was to be in command of the whole land force until Washington and Rochambeau arrived. Arrangements were made at once to land St-Simon's troops. Cornwallis saw them being ferried up the James River on 2 September, escorted by French frigates.