The mortar-fleet was under command of Admiral Porter, an able and energetic officer. He soon had his ships ready, and began moving them into position along the banks of the river, out of sight of the forts. To further conceal them from the gunners in the forts, he had the masts and rigging wrapped with green foliage; so that, lying against the dense thickets of willows that skirt that part of the river, they were invisible. Other boats that were in more exposed positions had their hulls covered with grass and reeds, so that they seemed a part of the swamp that bordered the river. After the line of fire had been obtained by a careful mathematical survey, Porter got all his mortar-boats into position, and began his bombardment. The gunners on the mortar-boats could not see the forts; but the range had been calculated for them, and they merely fired mechanically. A lookout, perched on the masthead, could see over the low willow-forest, and watch the course of the shells as they rushed high into the air, and then, falling with a graceful curve, plunged into the forts. The firing was begun on the 16th of April, and was kept up with a will. The twenty huge mortars keeping up a constant fire, made a deafening roar that shook the earth, and could be heard far up the river at New Orleans, where the people poured out into the streets, and gayly predicted defeat for any enemy who should attack "the boys in the forts." The forts were not slow in returning the fire; but as the mortar-vessels were hidden, and did not offer very large marks, their fire was rather ineffective. Parties of Confederates, old swamp-hunters, and skilled riflemen, stole down through the dense thickets, to pick off the crews of the mortar-schooners. They managed to kill a few gunners in this way, but were soon driven away by the point-blank fire of the supporting gunboats. But all this time the shells were falling thick and fast, driving the soldiers to the bomb-proofs, and tearing to pieces every thing unprotected. One shell set fire to some wooden structures that stood on the parade-ground in Fort Jackson; and, as the smoke and flames rose in the air, the gunners down the river thought that the fort was burning, and cheered and fired with renewed vigor. The shells that burst upon the levee soon cut great trenches in it, so that the mighty Mississippi broke through with a rush, and flooded the country all about. But the forts seemed as strong and unconquered as ever.