The next day she sailed for the mouth of the Mississippi, where, and at the head of the passes, the rest of the fleet was assembled, and Flag-Officer Farragut busily engaged in completing the preparations for the attack on New Orleans. The fleet consisted of four heavy sloops-of-war of the Hartford class; three corvettes of the Iroquois class; nine gunboats of the Cayuga class, and the large side-wheel steamer Mississippi, carrying in the aggregate one hundred and fifty-four guns, principally of nine-inch and eleven-inch calibre; but as the large ships carried their batteries mostly in broadside, the actual number that could be brought to bear, under the most favorable conditions, on every given point, would be cut down to the neighborhood of ninety guns. Supporting this force as auxiliary to it, for the bombardment of Forts Jackson and St. Philip, was Porter's mortar fleet of twenty schooners, each mounting a thirteen-inch mortar, and a flotilla of five side-wheel steamers, and the gunboat Owasco, carrying, in all, thirty guns. [Illustration: Map of the Mississippi River Showing Forts Jackson and St. Philip From the U.S. Coast Survey. Surveyed in 1870 by John N. McClintock.] The forts in question, forming the principal defences of New Orleans, were heavy casemated works with traverses on top for barbette guns, some ninety miles below the city at a point where the river makes a sharp bend to the southeast. Fort St. Philip, on the left bank, mounted forty-two guns, and Fort Jackson, including its water battery, had sixty-seven guns in position, all of calibre from the long twenty-four pounder to the heavy ten-inch Columbiad, and including several six-inch and seven-inch rifles. Stretching across the river from bank to bank to bar the channel, nearly opposite Fort Jackson and exposed to the perpendicular fire of St. Philip, were heavy ship's chains, supported and buoyed by hulks, rafts, and logs, and half a dozen large schooners. The rebels had also established some works on the banks of the river about four miles from town, known as the McGehee and Chalmette batteries, the latter being located at the point ever memorable in American history as the scene of General Jackson's overwhelming defeat of the British in 1815. Their reliance afloat was in the Louisiana, an ironclad, carrying nine rifles and seven smooth bores of heavy calibre; the ram Manassas, one gun; the McRae, seven guns; the Moore and Quitman with two guns each; six river steamers with their stems shod with iron to act as rams, and several iron-protected tugs.