It was in America that Ericsson won his greatest triumphs. He had invented a screw propeller for boats, and found a splendid market for this type of machinery. He built the steamship _Princeton_, the first screw steamer with her machinery under the water line. This was a great improvement on the old top-heavy style of steamboats, but how great was only to be known when war showed that ironclads with machinery safely sunk beneath the water line and so out of reach of the enemy's guns were to revolutionize naval warfare. By the time of the American Civil War men in all countries were experimenting with these new ideas for ships which Ericsson had launched upon the world. News came to Washington that the Confederate government had an all-iron boat, low in the water, which could ram the high-riding wooden ships of the Union navy, and would furnish little target for their fire. The Union was in great alarm, for it looked as though this small iron floating battery could do untold damage to the Union shipping. There was only one man to appeal to if the North were to offset this Southern ship, which had been christened the _Merrimac_. John Ericsson was the man, and he agreed to build an ironclad which should be superior to the _Merrimac_, and to build her in one hundred days. On March 8, 1862, the _Merrimac_ steamed into Hampton Roads, fully expecting to destroy the Union fleet there. But instead, to the great amazement of her officers and men a little iron boat, so small that she looked like a tiny pill-box on a plank, steamed out to meet her. She was so tiny it was almost impossible to hit her; she was almost entirely under water, and her gun turret was built to revolve so that she could fire in any direction. It was like a battle between David and Goliath, and when the day was over David had won, and the _Merrimac_ had to bow to the iron "pill-box" which had been named the _Monitor_. Proud was John Ericsson then, and rightly so, for he had invented an entirely new kind of ship, and one which was to give its name of _Monitor_ to all ships of its kind. The building of the _Monitor_ for its successful battle with the _Merrimac_ was the most dramatic incident in Ericsson's career as an inventor, but his whole life showed a series of wonderful inventions which for value and wide range can probably only be compared with those of Edison. The prophecy which the fairy had made to the shepherd in Sweden had come true, the name of Ericsson was known throughout the world. And in addition to John, the older brother Nils had won great renown in Sweden. He was made Director of Canals there, and created a nobleman for his great services to science and to his native land.