Also in the 1880s, it became possible to combine projectile and powder in a single round, using a brass cartridge case. When the gun was fired, the case expanded to seal the chamber against gas leakage. When the cartridge case cooled, it contracted, and it could be extracted relatively easily. Since it no longer had to seal the chamber very completely, the breech mechanism could be simplified and could operate much more rapidly. Cartridge cases had first been used in breech-loading rifles. In 1881 the Admiralty sought tenders for a 6pdr gun firing 12 rounds per minute. It was classified as quick-firing (QF). Initially it seemed that QF guns and their smaller cousins, machine guns and multi-barrel guns, were vital mainly as a defence against torpedo boats. However, within a few years larger-calibre QF guns were being produced, a 4.7in type being tested at Portsmouth in 1887. Some cruisers had their 6in guns converted to QF operation as QFC guns. Ironically, it soon turned out that a 6in gun with a ‘bare’ cartridge (i.e., without metal) could be made to fire quickly enough, using an improved breech mechanism, that QF operation was no longer needed above 4in or 4.7in calibre.
A second important development was much-improved gun mountings, which made it possible to fire even heavy guns quite rapidly. In the 1880s or early 1890s it seemed that a fast cruiser armed with heavy QF guns might tear up the sides of a battleship whose 12in or heavier guns might fire only once in several minutes. Soon after 1900 the same gun could fire once or twice a minute, and the big cruiser was much less viable, at least in a fleet action.
Steam Power34
Cruisers demanded a combination of high power (for speed) and long endurance at lower speed. All but one of the ships in this book were powered by reciprocating (piston) engines, and most of these engines were coupled directly to paddle wheel or, in most cases, propeller. Until engines and boilers became efficient, long endurance meant endurance under sail. Propellers or paddles created undesirable drag, and early screw cruisers were designed to hoist (retract) their propellers when they were not needed, and often also to collapse their funnels to make it easier to handle sail. That limited them to a single screw, and it demanded that space be left above the propeller into which it could retract (this space made it difficult to mount stern chasers).
The idea of the screw propeller originated well before 1800, but it became practicable only in the late 1830s. In England Francis Petit Smith built a 6-ton demonstrator, which ran successful sea trials for the Admiralty in 1838. Before adopting screw propulsion, the Admiralty asked for trials of a ship of at least 200 tons; Smith had the Archimedes built. Successful trials included a race across the Channel against the fastest of the paddle mail steamers of the time. By the spring of 1840 the Board was clearly convinced that the future lay with the propeller, and by 1844 the Admiralty was ordering screw frigates, although it continued to buy paddle warships.
Combining screws with wooden hulls entailed problems. A wooden hull flexed in a seaway, but the propeller shaft and its bearings had to be kept rigid over a considerable length (the French solved the problem using universal joints, but the British did not). As the propeller turned, its blades bit into the stream of water coming off the hull, causing the hull to vibrate. That vibration could damage a wooden hull. Finally, a bluff stern, such as that in a line of battle ship, could block the run of water to the propeller and thus make it inefficient. Propellers turned at higher speeds than paddles, so the engines driving them had to run at faster rates, and vibration became a problem. Once protective decks were introduced, cylinders had to be kept short enough to fit under those decks (initially the requirement was that the machinery lie completely below the waterline, where it was relatively safe from gunfire). Pistons had to run faster, and that increased vibration. In some ships cylinders were set horizontally, their dimensions limited by the ship’s beam.
Through the nineteenth century merchant ships, particularly the large Atlantic liners, led in engine and boiler development. The Admiralty naturally took a conservative point of view: it could not afford the consequences of large-scale failure. However, it did pioneer important improvements. In 1860 Engineer-in-Chief Thomas Lloyd told a Parliamentary Committee on marine engines that the Admiralty had led in the shift from flue to fire-tube boilers; the direct-acting instead of the beam engine; the screw propeller in place of paddles; and fast-running engines instead of slow-acting geared-up engines.35
The ships in this book burned coal. Each furnace was fed by hand, and a stoker could move only so much coal per hour. Boiler arrangements had to allow not only for stokers standing in front of them, but also for access to the mass of coal that each stoker used. Boiler spaces had to be massive, and high-powered ships needed large numbers of boilers. Coal was also an essential part of the protection of many British cruisers. Oil, whose advantages included ease of handling and a much higher energy content, was proposed as early as 1865, but was not adopted until after the turn of the twentieth century, mainly because coal was so much less expensive, and because large supplies of the best steaming coal were available in Wales.
As might be imagined, engines came in a bewildering variety of forms, which are not described in any detail in this book. Through the 1870s warship engines typically let into one or more cylinders (in parallel) and then condensed. Low-pressure steam did not have enough residual energy after the first expansion to be worth re-using. Some engines had double-acting cylinders, steam being let in alternately to one and then the other side of the single piston.
The associated boilers were, in effect, oversized teapots, vessels (often called boxes) filled with water and heated externally from below. Hot gas passed through flues below and around the mass of water and then up the funnel. Steam was drawn off at the top. These boilers could not withstand pressures much beyond 20lb/sq in (pounds per square inch, or psi); the boilers of the 1830s and 1840s operated at about 5psi. At such low pressures, engines operated by having their pistons driven by atmospheric pressure against a vacuum created when steam on the other side of a piston condensed. Boilers used sea water, which left a salt scale in them; it protected some iron parts (not the steam spaces, which pitted due to oxygen liberated from the water surface as it boiled) but also reduced heat transfer from flues to the water inside.
A 10in 18-ton muzzle-loading gun aboard HMS Sultan. This weapon armed the armoured cruisers Shannon, Nelson and Northampton. It was the heaviest muzzle-loader which did not require elaborate below-decks machinery for loading. The mounting is a pivoted slide, its rollers running along tracks (racers) laid in the deck. Slide carriages were common in the Royal Navy of the 1860s through the 1890s. Typically each gun port had a fighting bolt to which the front of the slide could be secured. In many cases guns could be rolled between sets of deck tracks (the installation in Sultan was clearly permanent, as it included a geared track) when the fighting bolt was disconnected. Often there was a permanent stowage bolt on the ship’s centreline, around which a gun pivoted to be placed at different ports. Once at the port, the stowage bolt was disconnected and the slide connected instead to the fighting bolt at the port. Guns were connected to the fighting bolts by pairs of bars carried on the slide. The gun carriage ran along the slide on gunmetal rollers. External compressor plates helped slow the gun’s recoil. The standard 64pdr 64cwt cruiser gun was mounted either on a truck or on a wooden (oak) slide, which moved on cross skids rather than on the metal rollers shown here. For the 18-ton gun, gearing elevated and traversed the gun, which recoiled along the slide. Ships later had more sophisticated Vavasseur pivot mountings in which gun and (shorter) slide were more integrated.
It seems to have been understood by the mid-1850s