The Canopus class was a group of six pre-dreadnought battleships of the British Royal Navy built in the late 1890s. The ships were designed by the Director of Naval Construction, William White, for use on the China Station. The class comprised , the lead ship, and , , , , and . The class was armed with a main battery of four BL 12 inch Mk VIII naval guns and a secondary battery of twelve QF 6-inch guns. Compared to the preceding s, the Canopus class was smaller, faster, and less heavily armoured, though they adopted new, stronger Krupp armour, which was more effective than the Harvey steel used in the Majestics. In addition to the Krupp steel, the ships also adopted several other changes, including water-tube boilers, in-line funnels, and a full-length armoured belt.
The six ships of the Canopus class served abroad for much of their early careers, with all six of them seeing service on the China Station in the early 1900s. In addition, Canopus also served with the Mediterranean Fleet during this period. In 1905, with the signing of the Anglo-Japanese Alliance, the Royal Navy withdrew most of its heavy units from the Far East, and the six Canopus-class ships returned to British waters, seeing further service with the Home, Channel, and the Atlantic Fleets through 1908. From then to 1910, most of the ships saw service with the Mediterranean Fleet, before being reduced to reserve status or other secondary duties thereafter.
With Britain's entry into the First World War in August 1914, the ships were mobilised as the 8th Battle Squadron, but they were quickly dispersed to other stations, serving as guard ships and convoy escorts. Canopus participated in the hunt for the German East Asia Squadron, which culminated in the Battle of the Falkland Islands in December 1914. In early 1915, most of the ships were sent to the eastern Mediterranean Sea to take part in the Dardanelles Campaign against the Ottoman Empire. During these operations, Ocean and Goliath were sunk, in March and May 1915, respectively. Canopus and Albion were withdrawn from active service in 1916, thereafter being used as barracks ships. Glory served as the flagship of the British North Russia Squadron, while Vengeance took part in operations off German East Africa in 1916. After the war, all four survivors were quickly broken up in the early 1920s.
Design
Design work began on what became the Canopus class in March 1895, when William Henry White, the Director of Naval Construction, presented the design for the Japanese s then being built in Britain to the Board of Admiralty. These ships, which were based on the British , represented a marked increase in Japanese naval power in East Asia, and White argued that more powerful battleships would be required on the China Station to counter them. He also suggested that the new design be capable of transiting the Suez Canal to reduce transit time between Europe and Asia. The Board concurred, and on 13 May again met White to provide their requirements for the new ships. Two days later, White relayed the parameters for the ships to his staff, along with instructions to prepare a suitable design as quickly as possible. The new ships were to have a freeboard equal to that of the battleship , the same main battery as the preceding s, a secondary battery of ten guns, the speed and fuel capacity as the second-class battleship , and an armoured belt that was 6 inches thick.
White and his staff prepared a preliminary design sketch on 23 May, which they submitted to the Admiralty. This vessel was to carry the specified battery of four guns and ten 6-inch guns on a displacement of . Speed was to be from . Further work to refine the design continued, and three variants were created: "A", "B", and "C". "A" reduced displacement slightly to , but kept the same armament and speed. "B" was broadly similar to the original design, but added two 6-inch guns, and "C" was slightly smaller, along the lines of "A", but its secondary battery consisted of eight 6-inch guns and eight guns. The three variants were submitted to the Admiralty in early October; on the 9th, the Board sent its reply to White, instructing him to prepare a new design that combined the armour layout of "A" and "B" with the secondary battery of "B".
Design work continued for almost a year before the final version was approved on 2 September 1896. By this time, the Board had decided to adopt new water-tube boilers after they had been successfully tested aboard the torpedo gunboat . The armour layout was further revised, with the final version discarding the thinner side armour above the belt, along with the aft strake of armour; the main and secondary guns also had their armour protection reduced. These reductions were used to increase the thickness of the forward strake and the main deck and to place four of the secondary guns in armoured casemates. Though the thickness of the armour layout was much reduced compared to the preceding Majestic class, the adoption of new Krupp steel in place of the Harvey steel allowed for only a modest decrease in protection.
Six vessels, rated as first-class battleships, were authorized to be built to the new design in the 1896 and 1897 estimates. Though the armour scheme was not as weak as it appeared on paper, the Royal Navy was not pleased with the reduction in defensive power. White's department regarded them as second-class battleships, and they were indeed classified as "improved Renowns" in the 1896 estimates. Nevertheless, they matched the Fujis they were intended to counter, and they represented the maximum offensive and defensive capabilities possible on the displacement and draught restrictions imposed by the Admiralty. They proved more than capable of performing the task for which they had been built on the China Station.
General characteristics
The ships of the Canopus class were long between perpendiculars and long overall, with a beam of . They had a draft of normally and up to fully loaded. They displaced normally and up to at full load. The ships were fitted with two masts, each with one fighting top carrying several of the light guns and one searchlight. Four other searchlights were mounted on the bridges.
Their crew numbered 682 officers and ratings on completion, but the number varied throughout the ships' careers. For example, by 1904, Goliaths crew had increased to 737 and Albion had a crew of 752, which included an admiral's staff. While serving as a gunnery training ship in 1912, Vengeance had a crew of just 400, while Albion was reduced to 371 officers and sailors as a guard ship in 1916. Each ship carried a number of small boats, including two steam pinnaces and one sail pinnace, one steam launch, three cutters, one galley, one whaler, three gigs, two dinghies, and one raft.
Propulsion The Canopus-class ships were powered by a pair of 3-cylinder triple-expansion engines that drove a pair of inward-turning screw propellers, with steam provided by twenty Belleville boilers. They were the first British battleships with water-tube boilers, which generated more power at less expense in weight compared with the fire-tube boilers used in previous ships. The new boilers led to the adoption of two fore-and-aft funnels, rather than the side-by-side funnel arrangement used in many previous British battleships. The Canopus-class ships proved to be good steamers, with a high speed for battleships of their time— from —a full two knots faster than the Majestics. The increase in speed came primarily from the water-tube boilers, which produced an extra compared to the older fire-tube boilers of the Majestics. The inward-turning screws also provided an increase in speed, since they could be operated at higher revolutions than the outward-turning screws used in earlier ships.
Each ship had a fuel capacity of of coal under normal conditions, but additional spaces could be used to double capacity, for during wartime. The ships burned of coal steaming at for 24 hours and up to at full speed every 24 hours. The Canopuses were able to reach at an economical cruising speed of with a full load of coal. While steaming at , the range fell significantly to .
Though the water-tube boilers significantly increased performance, they were plagued with problems throughout the ships' careers. Oceans boiler condenser tubes leaked badly until a refit in 1902–1903 corrected the problem. Vengeance similarly suffered throughout her service life, which reduced the efficiency of her engines. The inward-turning screws also caused problems in service, as they made steering difficult at low speed or when steaming in reverse; the arrangement proved to be unpopular with crews as a result. Regardless, the Royal Navy retained inward-turning screws in all future pre-dreadnought battleships, before returning to outward-turning propellers for in 1906.
Armament
The ships of the Canopus class had four 12-inch 35-calibre guns mounted in twin-gun turrets fore and aft; these guns were mounted in circular barbettes that allowed all-around loading, although at a fixed elevation. Canopus carried her guns in BIII mountings, the same used in the last two Majestic-class ships, while the next four vessels used the newer BIV mounts, and Vengeance used newer-still BV mountings. The BIII mounts featured a deck that interrupted the shell and propellant hoists to prevent the flash fire from an explosion in the turret from easily reaching down to the magazines, which could produce a catastrophic explosion. The BIV mounts eliminated this deck to allow for faster ammunition handling, but the designers realized the greatly increased risk this entailed, and so restored the deck with the BV mounts. To improve shell handling speed, a new turret was developed by Vickers for Vengeance that allowed for reloading the guns at all elevations, which eliminated the need to return to the fixed loading elevation, improving her rate of fire significantly.
The ships also mounted a secondary battery of twelve 6-inch 40-calibre guns mounted in casemates. Eight of the 6-inch guns were mounted in the main deck, which placed them too low to give them a good field of fire, though the other four guns, mount a deck higher, did not suffer from the same problem. For close-range defence against torpedo boats, the ships carried a tertiary battery of ten 12-pounder guns and six 3-pounder guns in individual mounts, distributed along the length of the ships, including in casemates in the bow and stern and in pivot mounts in the superstructure.
As was customary for battleships of the period, they were also equipped with four torpedo tubes submerged in the hull, two on each broadside near the forward and aft barbette. A fifth tube had been planned at the ship's stern, above the water, but it was eliminated during construction. This was likely done because the above-water tubes could not be adequately protected, and if a torpedo exploded while it was still in the tube, it could have done serious damage to the ship.
Armour
To save weight, Canopus carried less armour than the Majestics—6 inches in the belt compared to —although the change from Harvey armour in the Majestics to Krupp armour in Canopus meant that the loss in protection was not as great as it might have been, Krupp armour having 30 percent greater protective value at a given weight than its Harvey equivalent. Though it was thinner, it was more comprehensive; the Canopus class was the first British capital ship to return to a full-length armoured belt since , launched in 1875. To save weight, the belt was reduced to at either end of the ship. As with the belt, the other armour used to protect the ships could also be thinner; the bulkheads on either end of the belt were thick.