The effect produced abroad by the success of Ericsson’s _Monitor_ is so familiar to all that it hardly needs more than a passing allusion here. There is no doubt that the _Monitor_ was the progenitor of all the turreted vessels in the fleets of the world, though the essential principle of the vessel, however, was never viewed with favor. This principle consists in the low freeboard, which, besides reducing the size of the target, is intended to contribute to the steadiness of the hull as a gun-platform by offering no resistance to the waves that are expected to wash freely over the vessel’s deck: the horizontal overhang of the _Passaic_ class is intended to contribute to resisting a rolling motion. The vessel was designed to be as a raft on the water, constantly submerged by the passing waves, hermetically sealed to prevent the admission of water, and artificially ventilated by means of blowers drawing air down through the turret. This was the most startling feature about the construction. The protection afforded to the battery by a circular turret having the form best suited to deflect projectiles, the employment of machinery to point the guns by the rotation of the turret, the protection to motive power, to anchoring apparatus, etc., all presented admirable points of advantage, but the almost perfect immersion of the hull, and the absence of motion due to the _great stability_, are the essential features in the construction. [Illustration: U. S. DOUBLE-TURRETED MONITOR “TERROR.”] The double-turreted Monitors, of which the _Terror_ indicates the class, were built with a sponson, and it would have been better for the navy if this had been the only deviation made from the original design of Captain Ericsson. But it was not; the great mistake was made of building this class of Monitors of wood—a style of construction which had been already condemned abroad, in consequence of the impossibility of repairing an armored vessel so constructed, it being necessary to remove the armor for that purpose. The _Miantonomoh_, _Monadnock_, and _Terror_ were completed and put in commission. The _Miantonomoh_ made a cruise to European waters, spreading the fame of Ericsson, and proving the ability of a vessel of this type to navigate the high seas; the _Monadnock_ made the voyage to the Pacific, passing through the Strait of Magellan; and the _Terror_ was for a time on service on our eastern coast; but their lifetime was of short duration, and they are now being rebuilt, or rather new vessels, three of which bear their names, are now under construction of iron, which will serve to make them efficient and durable.