From the _Warrior_ to the _Inflexible_ the evolution of design was based upon a principle that sought the best results for the offence in small, powerful batteries, with all-around fire and armor protection; and for the defence, in thick armor carried over the vitals of the ship. This was satisfied by larger weights of armor and a smaller ratio of armored part to total surface. Wrought-iron armor was also replaced by compound, with a corresponding gain of twenty per cent. for equal thicknesses, and at present all-steel plates, of which great things may reasonably be expected, are now employed by France and Italy. In 1861 the _Minotaur_ was belted throughout her 400 feet of length with 1780 tons of armor, or with a weight nearly double that given to the _Warrior_ two years before. The _Inflexible_ has 3280 tons, and the _Trafalgar_ 4230 tons, of which 1040 are fitted horizontally. The maximum thickness of the _Warrior’s_ wrought-iron armor is 4½ inches, of the _Devastation’s_, 12 inches, and of the _Inflexible’s_ 24 inches; the compound (iron steel-faced) armor of the _Trafalgar_ is 18 and 20 inches thick, and the _Baudin_ and _Formidable_ have 21.7 inches in solid plates of steel. These, of course, are some of the dry-as-dust figures before referred to, and they are cited only to assist a comparison, their mere enumeration having no scientific value, because the disposition and character of the plates are unconsidered. To meet this development of offence and defence many changes in design have been adopted. The _broadside system_ of the first armored ships was followed in 1863-1867 by a _belt and battery type_, wherein the principal guns, much reduced in number, were carried in a box battery amidships, and given a fore-and-aft fire by means of recessed ports or outlying batteries. In 1869 the Admiralty adopted the _breastwork monitor_, a low free-boarded structure, which was plated from stem to stern in the region of the water-line, and had in its central portion an armored breastwork that carried at each end a revolving turret. In 1870 this type was pronounced unsafe, and after a careful investigation by a special committee on design certain modifications were recommended. These did not affect materially the essential features of Sir Edward Reed’s plan, for the complete water-line belt and the central armored battery were retained; and to-day many of the critics who then denounced it claim that, after all, it is the true type of an ideal battle-ship.