This clievaux de frise consisted of a line of sunken craft stretching across the stream, and it was hoped that the obstructions would at least detain the enemy's vessels long enough to admit of their being so destructively played upon by the Fori Washington and Fort Lee batteries as to compel them to turn back. It is true the batteries did some execution, killing and wounding men on each ship; but the obstructions in the river unfortunately began some distance from the shore, leaving an open space of tolerably deep water through which the expedition passed without difficulty and with little delay. The warships proceeded as far as Dobbs Ferry, and later moved up to Tarrytown, where they remained, wholly inactive, throughout the period of the eventful military operations in Westchester County. It does not appear thai they accomplished anything except the seizure of a few river craft carrying supplies to the American army, although incidentally they closed the navigation of the lower river to the Americans and perhaps diverted to the Hudson shore of Westchester County some troops that otherwise would have been used to strengthen the continental army. It is the general opinion of historical writers that the real purpose of the British commander in sending them tip the stream was to make a feint and cause the Americans to fix their attention upon the Hudson while he was preparing to outflank Washington from the Sound. The incident certainly did produce a vast deal of uneasiness on the We shall recur to this subject in detail later. American side. While Washington lay encamped on the Heights of Harlem, the whole southern border of Westchester County, stretching from Spuyten Duyvil Creek to the Sound, A\as protected by a large force under the efficient command of General Heath, with headquarters at Kingsbridge.