The two British Devastation-class battleships of the 1870s, and , were the first class of ocean-going capital ship that did not carry sails, and the first which mounted the entire main armament on top of the hull rather than inside it.
The ships were designed by Sir Edward Reed, whose concept was to produce short, handy ships of medium size as heavily armed as possible with a good turn of speed, that could attack and destroy an opponent without much risk of being damaged during the process.
Design and development
The Admiralty Design Board set forth the requirements for the ocean-going monitors. These included the requirement of two twin 12-inch gun turrets capable of firing 600-pound shells with a 280-degree firing arc. The turrets would require 14-inch armour protection, with the machinery spaces and shell rooms protected by 12-inch-thick armour. Further, to reduce the interference with the main guns, no masts or sails were needed. The ships would need two steam engines for security and a minimum 12-knot speed. The trans-Atlantic concept was changed to a coastal defence ship, so a very low freeboard of was specified.
The loss of in September 1871 led to concerns about the stability of turret ships, and a special committee was set up to determine their seaworthiness. Changes to the design were recommended. The freeboard of the design was increased to . Another change was to extend the armoured breastwork with un-armoured structure to the sides of the ship and carried aft to improve the stability at large angles of heel. This greatly improved the crew comfort by adding extra accommodation and especially latrines, but since it was not armoured it would have been riddled in a battle, reducing the stability of the vessel.
In 1871 a model of Devastation was tested in a water tank, and subsequently with an version. Once Devastation was completed, tests could be carried out with the real ship. This included building up a roll of 7 degrees by having 400 men run back and forth across the deck 18 times. Other tests involved taking it to sea to look for rough weather, in one trial waves of were encountered which gave the ship a 14-degree roll either way.
In 1872 the armour protection of the turret was subjected to a series of tests. A replica of the proposed turret was constructed and tested at Shoeburyness in May 1872. The armour plate backed by of teak and a metal skin resisted hits from a 25-ton 12-inch gun firing at a range of , although one shot hit a joint between plates and opened a gap wide but did not penetrate. A second test involved firing three shots at the turret of from a 25-ton gun at a range of 200 yards. The first shot missed, but the second and third shots struck the turret. The turret was not appreciably damaged, though theoretically it should have been penetrated.
Construction and specifications
Both vessels were laid down in 1869 at Portsmouth and at Pembroke. The Portsmouth ship was launched in 1870. Construction on the Pembroke ship was suspended following the loss of and not launched until 1872. They were in length between the perpendiculars with an overall length of . They had a beam of and a maximum draught of . They displaced . HMS Devastation was completed in 1873 and after a series of stability tests, HMS Thunderer was not completed until 1877 awaiting stability tests on HMS Devastation and a boiler explosion in 1876.
The machinery was initially supplied by Penn for the Portsmouth ship and Humphry's, Tennant & Company of Depford for the Pembroke ship. The ships were equipped with eight rectangular boilers powering two 2-cylinder trunk direct acting steam engines turning two shafts producing 6,650 indicated horsepower (IHP) under a natural draught (ND) for a designed speed of 13.75 knots. The ships carried 1,800 tons of coal giving a cruising range of 5,980 nautical miles at a nominal speed of 10 knots. The ships could remain at sea for approximately 12 days with fuel available to steam at full speed for a short duration.