While the antagonistic elements of offence, defence, speed, or endurance have caused the main differences of design in all types, the greatest variances with battle-ships are found in the distribution of armor for protection. A hasty summarization of the policies now adopted by the great maritime nations shows that the French generally adhere to a complete armor-belt at the water-line, that the Italians have in their latest ships totally abandoned side-armor, and that the English favor its partial employment. The popular idea that armor consists only of thick slabs of wrought-iron or steel, or of steel-faced iron, bolted to a ship’s side, is erroneous. “In the earlier broadside ships,” writes the present director of English naval construction, Mr. W. H. White, “this view was practically correct; they had no armor or protected decks, the decks being covered only by thin plates fitted for structural purposes. But in the _Devastation_ class, and all subsequent ships, considerable and increasing weights of material are worked into the deck armor, and with good reason. Experiments showed conclusively that horizontal protection at the top of the armor-belt, or citadel, was of vital necessity, and even now (1887) it is open to question whether the provision made for horizontal protection in relation to vertical armor is as large as it might advantageously be.” The factors which have most influenced the problem are the torpedo, ram, and gun. Of these the last is indubitably of the highest importance, for the number and nature, the effective handling, the disposition and command, and the relative protection of the guns are the elements which control most powerfully the principles of ship design. In the first stage of the contest between gun and armor the defence was victorious, but so rapidly have the art and science of ordnance developed that to-day the power of the heaviest pieces as compared with the resistance of the heaviest armor is greater than ever before.