Owing to the cramped space for training bow and stern-guns, and the necessity for rapid training, geared train-wheels are used in this slide in place of the regular training-tackle. A sunken rack in the deck, midway of the slide, forms the track for a heave mitre-wheel, the axle of which cants up to the rear and is held by a journal in the rear transom. On its outer end a large spur-wheel gears in an endless screw which is revolved by cranks. The axle of this endless screw also carries the windlass-drum for aiding the in and out tackle; it is therefore necessary that the screw and spur-wheel can ungear. For this purpose the main axle is in two parts, the rear one carrying a heavy sleeve which is free to revolve, and has a female screw-thread worked in it and handles outside for turning. A male screw-thread is worked on the forward axle, and the end is also slotted to allow a tenon on the after axle to fit it. By revolving the sleeve, then, the rear axle is pushed to the rear through the rear journal, thus releasing the spur-wheel from the screw. In this carriage there is also a slight modification of the arrangement for jamming the elevating-gear. There is also but one compressor-lever working as a ratchet-lever in a ratchet-wheel on the compressor-axle. The slide-rollers of this type are on concentric axles in action permanently. [Illustration: Slide Rear Roller, showing Manner of Pinning the Roller in Action.] _Slide-Carriage for the Long 21-cm. Gun, Pattern 1873._ [Illustration: (Plan.) (Section.) Stirrup on Carriage for Endless Chain.] [Illustration: Rear of Slide, showing Training-Gear, Chain-Roller, Crank, and Recessed Rear Roller for taking Recoil.] [Illustration: Axle-Grip for Putting Training-Gear in and out of Action.] [Illustration: Training-Axle and Rear Chain-Axle with Gearing.] [Illustration: Front Chain-Roller.] [Illustration: Recoil-Hook and Countersunk Traverse.]