The keel was laid on October 25, and on January 30, she slid down the ways into the water. A month later she was commissioned. The Monitor was 172 feet in length and displaced 776 tons. In the centre of her low flat deck was the revolving turret, twenty feet in diameter, protected by eight inches of iron-plating. Two heavy guns were mounted in the turret. The vessel was operated entirely by steam-engines, placed well below the water-line, which propelled a screw beneath the overhanging stern. Rushed to completion in the brief period of three months, the Monitor was barely commissioned in time to render, at Hampton Roads, the tremendous service which in a few brief hours revolutionized naval warfare, made obsolete the navies of the world, rescued the Union navy from crushing disaster, and immortalized the name of John Ericsson, her designer and constructor. The Monitor had been intended to serve with Admiral Farragut’s fleet at New Orleans, but a crisis nearer at hand made a sudden change of plans necessary. The Monitor left New York on the afternoon of March 6, 1862, under command of Lieutenant John L. Worden, U.S.N., and arrived at Hampton Roads on the evening of March 8, after a stormy passage. Meanwhile the armored Confederate ram Merrimac had created havoc with the great wooden warships of the Federal navy. On the seventh, the Merrimac had rammed and sunk the frigate Cumberland, and then destroyed the Congress, vessels powerless to inflict injury on the iron sides of the Confederate ram. The tall frigates, St. Lawrence, Roanoke, and Minnesota, powerless to resist or to escape, awaited their inevitable destruction on the following day. But on that eventful morning, as the Merrimac steamed out into the stream to complete her work, which would break the blockade the Federal forces had established, the Monitor glided out from under the stern of the Minnesota, looking for all the world like “a barrel-head afloat with a cheese-box on top of it.” For four hours these two strange vessels fought this greatest duel of naval history, which, on the ships and the shores, was watched by the anxious eyes of soldiers and sailors of North and South to whom the outcome was of such tremendous import. Manœuvring like boxers, the two vessels circled each other, black smoke pouring from their low funnels and the red flame of the great guns spurting from the gun-ports. As she had rammed the Cumberland, so did the Merrimac endeavor to crush the Monitor with her ram; but the Monitor either slipped past her heavier and more ungainly adversary or allowed the Merrimac to push her aside. Round and round the circular turret swung, turning away in order to load the two guns which protruded, and then swinging back to deliver a volley of metal against the plated sloping side of the Merrimac.