In addition to her armour the _Warrior_ was divided into 92 watertight compartments, fore and aft. She had a double bottom amidships, considerably subdivided (fifty-seven of the compartments), but no double bottom in the modern sense. The _Warrior’s_ engines, by Penn, were horizontal single expansion. On trial they developed 5,267 I.H.P., and the then excellent speed of 14.079 knots.[92] Her six hours’ sea speed trial resulted in a mean 5,092 H.P. and 13.936 knots. [Illustration: FRENCH LA GLOIRE WARRIOR & BLACK PRINCE HECTOR ACHILLES MINOTAUR NORTHUMBERLAND EARLY BRITISH BROADSIDE IRONCLADS] Save for her unprotected steering gear, the _Warrior_ may be described as a brilliant success for her era. She was launched on December 29th, 1860, and completed in the following year. The _Black Prince_ was completed in 1862. The _Warrior_ and _Black Prince_, under a system which long endured in the British Navy, were followed by a certain number of diminutives, of which the first were the _Defence_ and _Resistance_, of 6,150 tons, with speeds of just under 12 knots, and an armament of 16 guns. The armour was the same, but the battery protection was extended fore and aft, so that all guns were inside it. These ships were completed in 1862. Three more ships were projected, of which the _Hector_ and _Valiant_, completed in 1864 and 1865, were of precisely the same type as the _Resistance_, but displaced 6,710 tons, with about a knot more speed, and carried a couple of extra guns. A third ship, originally intended to have been of the same class, was the _Achilles_, but, mainly owing to the influence of Mr. Reed (of whom more anon), who pointed out the danger of unprotected steering gear, her design was altered and a complete belt of 4½-inch armour given to her instead of a partial one. Those changes in the design, together with an increased horse-power which produced on trial 14.32 knots, advanced the displacement of the _Achilles_ to 9,820 tons, while the armament was brought up to fourteen 12-ton guns and two 6½-ton. The weight of armour was 1,200 tons. The _Achilles_, like many another ship that was to follow her, was the “last word” of her own day. No expense was spared in seeking to secure a maximum of efficiency in her. As originally completed she was a ship-rigged vessel, but with a view to improving her sailing efficiency, this was subsequently altered to a four-masted rig, which proved so little successful that eventually she reverted to three masts again.