But the warship of John Ericsson in no way resembled the huge ironclads of France or England. With characteristic disregard for precedent he designed a ship which rested so low in the water that only about three feet of its sides would be exposed. The sides and deck were protected by heavy plates of iron, and in the centre of the deck was a circular heavily armored turret which revolved in either direction and contained powerful guns. These vessels, or monitors, as Ericsson named them, were to be propelled by steam. The particular advantages of the type were that so little of the craft showed above the water that it afforded an exceedingly small target to an enemy; that the heavy plating protected it from hostile shot, and the revolving target enabled the crew to fire in any direction without manœuvring the vessel, while such shot as might strike the turret would glance harmlessly from its circular side. During the Crimean War Ericsson offered the plans for this remarkable vessel to the French Emperor; but they were politely declined as impractical in much the same way in which, some years earlier, the British Admiralty had declined to consider the screw-propeller as little more than an amusing experiment. When war was declared in 1861 between the Northern States and the Confederate States of the South, Ericsson was fifty-eight years old. In this national calamity in which brother was armed against brother, and the fate of the country seemed hanging by a thread, Ericsson unhesitatingly cast himself with those who sought the preservation of the Union and the abolition of slavery from the United States. Never before had his adopted country needed so vitally his tremendous services. With superb health derived from a normal life of conservative habits, and a brain trained by long years of engineering experiment, Ericsson found himself ready and able to meet the call for his greatest service to the nation. The United States navy at the beginning of the war was composed entirely of wooden vessels. Early in 1861 the Confederates began the construction of a floating battery heavily armored with iron. For this purpose the old United States frigate Merrimac, which had been burned and sunk in the Norfolk Navy Yard, was raised, and the work of encasing her with armor plates was begun. Meanwhile, in the North, Congress had called for proposals for ironclad steam vessels, and less than a month later, Ericsson addressed to President Lincoln a letter in which he offered to submit the plans of a monitor, and described the advantages of its unique design. On September 13, Ericsson went to Washington and personally laid before the Navy Department his plans and received a contract to proceed with the construction of the Monitor.