The only difference between these and the others is that the slide is much higher and is centre-pivoting. In order to take off the shock of recoil from the pivot-bolt, the slide-rollers overlap the circles on both sides. _Slide-Carriage for the 30½-cm. Gun for Armored Gun-boats._ The general principle of the carriage is the same as the ordinary one. Its front and rear rollers are the same, and the elevating-gear is the rack and pinion type, the power being increased in accordance with the greater weight to be moved. The carriage is heavier braced, having three transoms in place of two. There are no out-tackles or chain-gearing, the slope of the slide (6°) being sufficient to run the gun out by its own weight. When it is necessary to run it in, in-tackles are used, the falls being taken over windlass-heads on the rear hurter of the slide. The slide is centre-pivoting, and traverses on four heavy rollers which overlap the edges of the circles to take the force of the recoil. A cramp under the forward end of the slide moving in an undercut circle on deck also takes the recoil shock. The gun is traversed by gearing. Just inside the roller-circles is a circular rack into which a pinion gears; the inner end of the pinion-axle carries a mitre-wheel whose upper and lower cogs gear in mitre-pinions which are worked on loose sleeves on a vertical axle. Between these pinions, revolving with the axle, but free to move vertically, is an iron grip which catches in the upper or lower pinion, according as it is desired to sweep the gun to the right or left. The vertical axle passes down to the lower deck, where is a train-work with crank-handles to be revolved by six men. By means of the single grip arrangement between the mitre-pinions, the gun may be traversed to the right or left or stopped without reversing the motion of the crank-handles below. The hydraulic recoil cylinder above described is used to check the recoil and control the running out of the gun. A sheet-iron musket-proof shelter is raised on the slide for the protection of the gun’s crew. For lifting the projectile to the gun a derrick is fixed at the rear of the slide. The fall of the whip is taken around a windlass-head, and the davit is swung around by means of an endless screw and pinion. [Illustration: Front Half of Slide for Centre-Pivoting Gun-boat Carriage.] [Illustration: Gear below Deck for Revolving Gun-boat Carriage.] _Turret-Carriage for the 21-cm. Gun (Arminius)._ [Illustration: Turret-Carriage for Minimum Port. (See next page.)]