After Robert Fulton's invention of the steamboat in 1807 there were many attempts to apply steam on vessels of war. But it was a long time before these attempts were very successful. The earliest war steamships were driven by paddle-wheels, placed at the sides of the vessels. The paddles, besides taking up much valuable space, were exposed to the shots of the enemy, and in any battle were very easily crippled and made useless. But the speed of these vessels was much greater than that of any sailing ship, and this alone made them very desirable. For many years steam frigates were the most formidable vessels in the navy. The first successful steamship of war was the English frigate _Penelope_, which was built in 1843, and carried forty-six guns. One of the earliest and most noted American vessels of the same type was the _Powhatan_. The first screw line of battle ship was built by the French in 1849. It was called the _Napoleon_, and carried one hundred guns. It was so successful that steamships soon began to take the place of sailing vessels in all the navies of the world. [Illustration: THE MERRIMAC AND THE MONITOR.] Up to this time all war vessels were built of wood; but there had been many experiments to learn whether they might not be protected by iron plating. The first iron-clad ship was built in France in 1858; and not long after that Great Britain added to her navy an entire fleet of iron-clads. All these were built after the same pattern as wooden ships, and were simply covered or protected with iron plates. [Illustration: THE BATTLESHIP OREGON.] The first iron-clads used in our own navy were built soon after the beginning of the Civil War (1861), and were designed for use on the large rivers and along the coast. They were called "turtle-backs," and were simply large steamboats covered with thick slabs of iron and carrying thirteen guns each. The iron slabs were joined closely together and laid in such a manner as to inclose the decks with sloping sides and roofs. The first great deviation from old patterns was the _Monitor_, built by John Ericsson in 1862. She was the strangest looking craft that had ever been seen, and has been likened to a big washtub turned upside down and floating on the water. The _Merrimac_, which she defeated in Hampton Roads, was a wooden frigate which the Confederates had made into an iron-clad by covering her with railroad rails. They had also, by giving her an iron prow, converted her into a ram. These two vessels, the _Monitor_ and the _Merrimac_, were indirectly the cause of a great revolution in naval warfare; they were the forerunners of all the modern ships of war now in existence. The nations of the world saw at once that there would be no more use for ships of the line and wooden frigates and sloops of war. [Illustration: THE DYNAMITE CRUISER VESUVIUS.]