As a matter of course, notice was immediately given to all foreign vessels in port of the proposed blocking of the Narrows and the Main, Swash and East Channels with torpedoes, and forty-eight hours' time was accorded them wherein to take their departure. The European steamers were the first to leave, each one towing from two to five sailing-vessels. Later on, General Hancock impressed all the harbor tugs into service; and, by their aid, before the specified period had elapsed, not a single ship floating a foreign flag remained in New York Harbor. A battalion of army engineers, under command of General Abbot, and another of sailors, under Captain Selfridge, at once began operations. In the Narrows, torpedoes were moored at distances of one hundred feet apart, and were connected with the shore by electric wires. At various points along the beach shell-proof huts were constructed, to which these wires led. In each hut was arranged a camera lucida, so that a picture of the harbor, over a limited area, was thrown upon a whitened table. In this way an observer could recognize the instant an enemy's vessel arrived over a sunken mine, and could explode the latter by simply touching a button which allowed the electric current to pass to the torpedo. In the Harbor channels the torpedoes were so arranged as to be exploded on contact of an enemy's vessel with a partially submerged buoy. The torpedo-stations on Staten and Coney Islands and the Jersey coast were provided with movable fish-torpedoes of the Ericsson and Lay types, intended to be sent out against a hostile vessel, and manoeuvred from the shore. All the steam-tugs in the Harbor were moored in Gowanus bay, and each tug was rigged with a long boom projecting from her bow, on which a torpedo, containing some fifty pounds of dynamite, was carried. With the tugs, and serving as flag-ship for the squadron, was the U.S. torpedo-boat "Alarm," Lieutenant-Commander H.H. Gorringe. The armament of the sea-coast batteries was not calculated to strike terror into the soul of any nation owning a modern ironclad vessel. It consisted mainly of old-fashioned smooth-bore guns, a system of artillery which has been rejected by every European power as the weakest and most inefficient. The greatest range attainable with the best of these cannon was 8000 yards, or some four and one half miles. At one quarter this range their shot would be utterly unable to penetrate even moderately thin armor. Besides these guns there were a few ten and twelve-inch rifles of cast-iron, and hence of unreliable and inferior material; some old smooth-bore cannon, converted into rifles by wrought-iron linings; and a number of mortars and pieces of small calibre, altogether contemptible in the light of the advances made in the art of war during the last quarter of a century.