The Leander class was a four-ship cruiser programme ordered by the Admiralty in 1880. The class comprised , , , and .
Genesis
"A new and better policy of unarmoured construction was inaugurated by the Admiralty of 1874-80. They began by building the two despatch vessels, and , with a speed not approached up to that date by any in naval service. In the Mercury and the Iris, the speed was obtained by an enormous development of horse-power… The cost per ton was equal to that of the most powerful ironclad, while the fighting power was inconsiderable."
In 1880, the Admiralty Board were divided about next design of cruising ship to lay down. The First Naval Lord, Sir Astley Cooper Key, favoured an enlarged . Some of the other members of the board preferred an improved . The First Lord of the Admiralty, William H. Smith, backed the latter. A change of government occurred on 23 April 1880; Lord Northbook replaced W.H. Smith as First Lord, though Astley Cooper Key continued as First Naval Lord. "Lord Northbook's board were deeply impressed with the necessity for developing the construction of vessel of the Leander" type. "The first four ships of a large class laid down for the protection of commerce under Lord Northbrook's board were of the Leander type. The Leanders have a displacement of 3,750 tons. Their speed is 17 knots… Their coal supply is 1016 tons. These ships were followed by the four ships of the Mersey type…"
The Leanders were primarily designed for trade protection. In 1881, it was argued that Britain had fallen behind in cruisers to protect Britain's mercantile marine, which at the time was at least half the world total. "Taking 14 knots as the standard of high speed, we have only 11 swift cruisers, counting the Iris and Mercury despatch vessels among them. Fine vessels they are, and no doubt the and the , when they have got on board their new armament, will give a good account—a very good account indeed—of any cruiser in the world that is not an iron-clad. But the world is a large place; and eight or ten vessels cannot be everywhere, and the safety of our commerce imperatively demands that the swift cruisers which we have ready at the outbreak of a war shall be enough to clear the seas of privateers. Much use, as a war goes on, may, no doubt, be made of the armed merchantmen on the Admiralty List; but we must have Royal [Navy] cruisers to begin with, A commencement was made last year by the late Board in the Leander and her two consorts, which, with their partially protected machinery, their great speed, and their excellent guns, will be everything that can be desired for the purpose for which they were devised. The present Board have carried this policy farther. We are pushing on the Leanders, and we have laid down a fourth Leander at Pembroke, to occupy the spare time of the 200 extra men who are working on the iron-clads…"
On 2 December 1884, the Secretary to the Admiralty stated, "The present Board have been gradually developing, and, as I would venture to say, in an effective manner, our resources for the protection of commerce. The late Board of Admiralty laid down an admirable type for the purpose in the Leander class. We have followed in their footsteps by producing the Mersey type, and we now propose to go a step further in the same direction, by laying down vessels of the Mersey class, but protected by a belt in lieu of an armoured deck. The belt will, I think, be approved by my hon. Friend who sits behind me (Sir Edward J. Reed)." These belted cruisers were the .
Design
Compared with the Iris class, the designers of the Leander "cut down top hamper and took advantage of the recent advance in gun construction to reduce the weight of, while adding to the efficiency of armaments. The models approved for the new ships were favourable to high speed."