The ''Iris'' class consisted of two ships, and , built for the

Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...

in the 1870s. They were the first British all-steel

warship A warship or combatant ship is a naval ship that is built and primarily intended for naval warfare. Usually they belong to the armed forces of a state. As well as being armed, warships are designed to withstand damage and are usually faster a ...

Design and description

The ''Iris''-class ships were designed as dispatch vessels by William White under the direction of

Nathaniel Barnaby Sir Nathaniel Barnaby, (25 February 1829 – 16 June 1915) was Chief Constructor of the Royal Navy from 1872 to 1885. Biography Born on 25 February 1829 in Chatham, Barnaby began his career as a naval apprentice at Sheerness in 1843. He won a ...

Director of Naval Construction The Director of Naval Construction (DNC) also known as the Department of the Director of Naval Construction and Directorate of Naval Construction and originally known as the Chief Constructor of the Navy was a senior principal civil officer resp ...

, and were later redesignated as second-class

protected cruiser Protected cruisers, a type of naval cruiser of the late-19th century, gained their description because an armoured deck offered protection for vital machine-spaces from fragments caused by shells exploding above them. Protected cruisers re ...

s. 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 The bow () is the forward part of the hull of a ship or boat, the point that is usually most forward when the vessel is underway. The aft end of the boat is the stern. Prow may be used as a synonym for bow or it may mean the forward-most part ...

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 __NOTOC__ Length overall (LOA, o/a, o.a. or oa) is the maximum length of a vessel's hull measured parallel to the waterline. This length is important while docking the ship. It is the most commonly used way of expressing the size of a ship, an ...

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 Maudslay, Sons and Field was an engineering company based in Lambeth, London. History The company was founded by Henry Maudslay as Henry Maudslay and Company in 1798 and was later reorganised into Maudslay, Sons and Field in 1833 after his sons ...

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 A drive shaft, driveshaft, driving shaft, tailshaft (Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power and torque and rotation, usually used to connect ...

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 A sea trial is the testing phase of a watercraft (including boats, ships, and submarines). It is also referred to as a "shakedown cruise" by many naval personnel. It is usually the last phase of construction and takes place on open water, and i ...

, 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 A barque, barc, or bark is a type of sailing ship, sailing vessel with three or more mast (sailing), masts having the fore- and mainmasts Square rig, rigged square and only the mizzen (the aftmost mast) Fore-and-aft rig, rigged fore and aft. Som ...

sailing rig, but this was removed after a few years. The ''Iris''-class ships were originally armed with ten 64-pounder () rifled muzzle-loading ( RML) guns, eight on the

main deck The main deck of a ship is the uppermost complete deck extending from bow to stern. A steel ship's hull may be considered a structural beam with the main deck forming the upper flange of a box girder and the keel forming the lower strength memb ...

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