But Great Britain was not content with the _Dreadnought_, for each succeeding ship or set of ships was improved until, only four years later, there was launched the _Orion_ already referred to, nearly 5000 tons bigger, with 2500 more horse-power, and with 13½-inch guns instead of 12-inch. The _Orion_ and her sisters are often spoken of as super-Dreadnoughts. The Dreadnoughts as a class are often referred to as "all-big-gun" ships, since that is the feature which most distinguishes them from those which went before. These large guns are mounted in turrets as they are called. We might describe these as turn-tables with a cover over something like a small gas-holder. There are usually two guns in each turret, although there are a few ships whose turrets have three in each. The turrets seem to be standing on the deck of the ship and it is by turning them round that the guns are trained or pointed at their target. The original _Dreadnought_ had one turret in front and two behind, all on the centre-line of the ship, and two more, one each side, amidships. In late vessels all five turrets are on the centre-line. Thus the _Dreadnought_ can fire six guns ahead, eight astern and eight to either side, while the newer ships can fire four ahead, four astern and all ten on either side. There are other battleships with even more guns than these, such as the U.S.A. ship _Wyoming_, with twelve 12-inch guns, but the British Navy seems to prefer to stick to the original number of ten. The reason for this is that every such ship is a compromise between three alternatives. The three great features have already been pointed out, namely, the guns, the armour and the propelling machinery. Either of these can be increased at the cost of one or both of the others, but all cannot be increased without sinking the ship, unless indeed, the ship be made larger and then other considerations crop up. And that brings us to another class of ship often ranked among the battleships. These remarkable vessels are also termed cruisers and the fashion seems to have established itself of combining the two names and calling them battle-cruisers. They gave a fine account of themselves during the war. The first three of these, of which the _Invincible_ is usually taken as the type, made its appearance the year after the _Dreadnought_, and like the latter were the offspring of the fertile brain of Lord Fisher. The _Invincible_ was about the same size as the _Dreadnought_, but had nearly twice the horse-power (41,000), which enabled it to attain an actual speed of nearly six knots more, namely, 28·6. For guns it had eight of the same large weapons, and it was armoured with 7-inch steel armour-plates instead of 11-inch. Thus we see illustrated what has just been said, less guns and thinner armour, to allow for more engine power and higher speed. Or, to put it the other way, we observe how higher speed was attained at the expense of the guns and the armour.