were very thick, and for which there was much experience. With an iron-hulled ship the "bottom is without any doubt very thin and liable to penetration by a rock or any other hard substance; but the danger resulting from penetration is very greatly reduced by the adoption of a proper number of watertight divisions or bulkheads in the ship's hold, while it may be almost got rid of by the cellular bottom, now given to all our iron-clads, which prevents the entrance of water into the hold even when the outer plating is penetrated." It should be added that before the introduction of the bracket-frame system with the Bellerophon, double-bottoms on British iron-hulled iron-clads were very partial. Armour "In our earlier iron-clads the protection is only partial, extending over a portion of the length of the broadside. No better example of this system can be chosen than the Warrior. Her length is 380 feet, and the armoured portion is only 213 feet in length, the extremities of the ship being left entirely unprotected... The rudder head and steering apparatus are left entirely unprotected. This system of partial protection is also adopted in the Black Prince, Defence, and Resistance; but the desire to increase the amount of protection led to the introduction into the Hector and Valiant of a modification of the Warriors disposition of armour. This modification consisted in adding a belt of plating, extending from the upper to the main decks, before and abaft the main portion of the broadside armour, which was arranged similarly to Warriors. The main deck, on which the guns are fought, is thus protected throughout the entire length, but the extremities 'between wind and water' are quite as unprotected as those on the Warrior". "Both these plans of disposing the armour were afterwards considered unsatisfactory, and resort was had in the , and in the converted ships of the Caledonia class, to the system of which had been introduced into the construction of the floating batteries built during the Crimean war, by means of which what is known as 'complete protection' is secured. Throughout the length the armour extends from the upper deck down to about 6 feet below the waterline... The principal advantages possessed by this disposition of the armour over that of the Warrior are that the extremities of the ship, especially on the parts near the water-line, are iron-cased, and that