With the exception of the vessels already employed on the blockade, the flag-ship was the first to arrive of the force destined to make the move up the river. One by one they came in, and were rapidly assembled at the Southwest Pass, those whose draught permitted entering at once; but the scanty depth of water, at that time found on the bar, made it necessary to lighten the heavier vessels. The Pensacola, while at Ship Island, chartered a schooner, into which she discharged her guns and stores; then taking her in tow went down to the Pass. She arrived there on the 24th of March and made five different attempts to enter when the water seemed favorable. In the first four she grounded, though everything was out of her, and was got off with difficulty, on one occasion parting a hawser which killed two men and injured five others; but on the 7th of April, the powerful steamers of the mortar flotilla succeeded in dragging her and the Mississippi through a foot of mud fairly into the river. These two were the heaviest vessels that had ever entered. The Navy Department at Washington had hopes that the 40-gun frigate Colorado, Captain Theodorus Bailey, then lying off the Pass, might be lightened sufficiently to join in the attack. This was to the flag-officer and her commander plainly impracticable, but the attempt had to be made in order to demonstrate its impossibility. After the loss of a fortnight working she remained outside, drafts being made from her crew to supply vacancies in the other vessels; while her gallant captain obtained the privilege of leading the fleet into action, as a divisional officer, in the gunboat Cayuga, the commander of the latter generously yielding the first place on board his own ship. A fleet of twenty mortar-schooners, with an accompanying flotilla of six gunboats, the whole under the command of Commander (afterward Admiral) David D. Porter, accompanied the expedition. Being of light draught of water, they entered without serious difficulty by Pass a l'Outre, one of three branches into which the eastern of the three great mouths of the Mississippi is subdivided. Going to the head of the Passes on the 18th of March, they found there the Hartford and Brooklyn, steam sloops, with four screw gunboats. The steam vessels of the flotilla were at once ordered by the flag-officer to Southwest Pass, and, after finishing the work of getting the heavy ships across, they were employed towing up the schooners and protecting the advance of the surveyors of the fleet. The squadron thus assembled in the river consisted of four screw sloops, one side-wheel steamer, three screw corvettes, and nine screw gunboats, in all seventeen vessels, of all classes, carrying, exclusive of brass howitzers, one hundred and fifty-four guns. Their names and batteries were as follows: