On Sept. 3, yet another attack upon the town and fortress was made. As in the foregoing instances, nothing was accomplished except the throwing of a vast quantity of shot and shell. Capt. Bainbridge, in a secret letter to Preble, reported, that of the shells he had seen falling in the city very few exploded, and the damage done by them was therefore very light. Preble investigated the matter, and found that the fuse-holes of many of the shells had been stopped with lead, so that no fire could enter. The shells had been bought in Sicily, where they had been made to resist a threatened invasion by the French. It is supposed that they had been thus ruined by French secret agents. But, before this time, Commodore Preble, and the officers under his command, had about reached the conclusion that Tripoli could not be reduced by bombardment. Accordingly they cast about for some new method of attack. The plan that was finally adopted proved unfortunate in this instance, just as similar schemes for the reduction of fortresses have prove futile throughout all history. Briefly stated, the plan was to send a fire-ship, or rather a floating mine, into the harbor, to explode before the walls of the fortress, and in the midst of the enemy's cruisers. The ketch "Intrepid," which had carried Decatur and his daring followers out of the harbor of Tripoli, leaving the "Philadelphia" burning behind them, was still with the fleet. This vessel was chosen, and with all possible speed was converted into an "infernal," or floating mine. "A small room, or magazine, had been planked up in the hold of the ketch, just forward of her principal mast," writes Fenimore Cooper. "Communicating with this magazine was a trunk, or tube, that led aft to another room filled with combustibles. In the planked room, or magazine, were placed one hundred barrels of gunpowder in bulk; and on the deck, immediately above the powder, were laid fifty thirteen-and-a-half-inch shells, and one hundred nine-inch shells, with a large quantity of shot, pieces of kentledge, and fragments of iron of different sorts. A train was laid in the trunk, or tube, and fuses were attached in the proper manner. In addition to this arrangement, the other small room mentioned was filled with splinters and light wood, which, besides firing the train, were to keep the enemy from boarding, as the flames would be apt to induce them to apprehend an immediate explosion." Such was the engine of death prepared. The plan of operations was simply to put a picked crew on this floating volcano, choose a dark night, take the "infernal" into the heart of the enemy's squadron, fire it, and let the crew escape in boats as best they might.