The arrival of the vast fleet, the subsequent landing of an army of nearly twenty-five thousand men, and the warlike preparations which the British were feverishly making looking to the capture of the city, did not alarm Old Put, with his total force of scarcely seventeen thousand. He went on as calmly and as determinedly as though himself commander of the larger army, for the hero of Bunker Hill never anticipated defeat. He always fought to the last, after making every needful preparation for whatever event, and at New York, although the chances were all against him, he did his utmost to bring about success. He had fortified Governor's Island and Red Hook in order to prevent the enemy's ships of war from ascending the Hudson; he now sank several old hulks in the channel for the same purpose; but, notwithstanding, two war-vessels succeeded in getting up the North River, which they afterward descended, without injury to themselves. It having been recommended by Congress that "fire-rafts be prepared and sent among the enemy's shipping," Putnam acted in accordance with the suggestion by fitting out fourteen fire-ships for the purpose, though nothing was accomplished with them. Still persistent in his endeavors to drive off the enemy, he adopted the invention of David Bushnell, a native of his own State, which the inventor called the "great American Turtle," and which, in fact, was a submarine torpedo, probably the first one thus used in warfare. It was to be guided by one man, and that man was to have been Bushnell himself; but, unfortunately, he fell sick, and the "turtle" boat with its infernal machine was entrusted to a Connecticut sergeant named "Bije" Shipman, who promised to row the "submarine"--diminutive prototype of all those which have committed such destruction since--down the bay and attach the torpedo to the bottom of the British admiral's ship. He reached the ship without being observed--strange to say--and attempted to attach the torpedo; but the attaching screw struck against an iron plate and caused great delay. Coming up to get a breath of fresh air, "Bije" was seen and fired upon by a sentinel, and at once rowed away as fast as his oars could carry him. The torpedo, the explosion of which was regulated by clockwork operating on a gun-lock, actually exploded about half an hour after, sending up a great geyser of water, which frightened the British admiral so that he gave orders to up anchor and seek another mooring-place.