The ''Iris'' class consisted of two ships, and , built for the Royal Navy in the 1870s. They were the first British all-steel warships.

Design and description

The ''Iris''-class ships were designed as dispatch vessels by William White under the direction of Nathaniel Barnaby, Director of Naval Construction, and were later redesignated as second-class protected cruisers. The only visible difference between the

sister ship A sister ship is a ship of the same class or of virtually identical design to another ship. Such vessels share a nearly identical hull and superstructure layout, similar size, and roughly comparable features and equipment. They often share a ...

s was that had a clipper bow and was longer than with her straight

stem Stem or STEM may refer to: Plant structures * Plant stem, a plant's aboveground axis, made of vascular tissue, off which leaves and flowers hang * Stipe (botany), a stalk to support some other structure * Stipe (mycology), the stem of a mushro ...

. ''Iris'' was long overall while ''Mercury'' was long. The sisters had a beam of , and a draught of . They displaced at normal load and were the first British warships with an all-steel hull.Gardiner, p. 90 Their crew consisted of 275 officers and ratings.Lyon & Winfield, p. 270 The ships were not armoured but extensive internal subdivision gave them some protection against flooding, as did the

double bottom A double hull is a ship Hull (watercraft), hull design and construction method where the bottom and sides of the ship have two complete layers of watertight hull surface: one outer layer forming the normal hull of the ship, and a second inner hull ...

under the propulsion machinery compartments. The ''Iris'' class was powered by a pair of horizontal four-cylinder Maudslay, Sons and Field compound-expansion steam engines that were configured with a pair of high-pressure cylinders with a

bore Bore or Bores often refer to: *Boredom * Drill Relating to holes * Boring (manufacturing), a machining process that enlarges a hole ** Bore (engine), the diameter of a cylinder in a piston engine or a steam locomotive ** Bore (wind instruments), ...

of and a pair of low-pressure cylinders in diameter. All cylinders had a

stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

. Each engine drove one propeller shaft using steam from eight oval and four cylindrical boilers with a working pressure of . The engines were designed to produce a total of for a speed of , which was handily exceeded by the sisters. ''Iris'' initially reached a maximum speed of from during her sea trials, but after new propellers were fitted, achieved from . ''Mercury'' became the fastest warship in the world when she made from .Roberts, p. 74 The ships carried a maximum of of coal, enough to steam at . They were initially fitted with a barque sailing rig, but this was removed after a few years. The ''Iris''-class ships were originally armed with ten 64-pounder ()

rifled muzzle-loading A muzzle-loading rifle is a muzzle-loaded small arm or artillery piece that has a rifled barrel rather than a smoothbore. The term "rifled muzzle loader" typically is used to describe a type of artillery piece, although it is technically accurate fo ...

( RML) guns, eight on the main deck and the remaining pair on the upper deck on

pivot mount A pivot gun was a type of cannon mounted on a fixed central emplacement which permitted it to be moved through a wide horizontal arc. They were a common weapon aboard ships and in land fortifications for several centuries but became obsolete aft ...

s to serve as

chase gun A chase gun (or chaser), usually distinguished as bow chaser and stern chaser, was a cannon mounted in the bow (aiming forward) or stern (aiming backward) of a sailing ship. They were used to attempt to slow down an enemy ship either chasing ( ...

s fore and aft.

Ships

Construction and career

''Iris'' was launched in 1877 and sold in 1905 while ''Mercury'', launched a year later, was hulked at Chatham in 1914 and sold for scrap in 1919.

Citations

Bibliography

* * * {{Iris class cruisers Cruiser classes Ship classes of the Royal Navy