Editing Invincible-class battlecruiser (section)

==Design==
After Admiral Fisher was appointed [[First Sea Lord]] on 20 October 1904, he pushed through the [[British Admiralty|Board of Admiralty]] in early December 1904 a decision to arm the next armoured cruiser with {{convert|12|in|0|adj=on}} guns and that it would have a speed no less than {{convert|25.5|kn|lk=in}}. Shortly afterwards he convened a "Committee on Designs" to investigate and report on requirements for future ships. While nominally independent, it served to validate decisions already made and to deflect criticism off Fisher and the Board of Admiralty, as it had no ability to consider options other than those already decided upon by the Admiralty. Fisher appointed all of the members of the Committee and himself as President of the Committee. During its last meeting on the 22 of February 1905 it decided on the outline design of the fast armoured cruiser. This, in turn, was approved by the Board on March the 16th with only minor changes, such as the reduction in the anti-[[torpedo boat]] armament from twenty to eighteen [[QF 12 pounder 12 cwt naval gun|12-pdr]] guns.<ref>Roberts, pp. 18–20, 22–24</ref>

===General characteristics===
The ''Invincible''-class ships were formally known as armoured cruisers until 1911, when they were redesignated as battlecruisers by an Admiralty order of 24 November. Unofficially a number of designations were used until then, including cruiser-battleship, dreadnought cruiser and battle-cruiser.<ref>Roberts, pp. 24–25</ref>

The ''Invincible''s were significantly larger than their armoured cruiser predecessors of the {{sclass|Minotaur|cruiser (1906)|4}}. They had an [[length overall|overall]] length of {{convert|567|ft|m|abbr=on}}, a [[beam (nautical)|beam]] of {{convert|78.5|ft|m|abbr=on}}, and a [[draft (ship)|draft]] of {{convert|30|ft|m|1|abbr=on}} at deep load. They displaced {{convert|17250|LT|MT}} at load and {{convert|20420|LT|MT}} at deep load, nearly {{convert|3000|LT|MT|-1}} more than the earlier ships.<ref>Roberts, pp. 43–44</ref>

===Propulsion===
Early in the design process the "Committee on Designs" had thought to power these ships with the traditional reciprocating vertical [[Marine steam engine#Triple or multiple expansion|triple-expansion steam engines]], but were persuaded to adopt [[Parsons Marine Steam Turbine Company|Parsons]] [[steam turbine]]s as they required fewer boilers for the same amount of power, were easier to protect from damage as they were more compact than reciprocating engines and could be kept below the waterline. In addition they were significantly lighter and more reliable than the older design. The [[Direct-drive mechanism|direct-drive]] turbines then in use did have one significant drawback in that they ran at a relatively high speed which required small-diameter, fine-pitch propellers of a large blade area which adversely affected manoeuvrability at low speeds. [[Charles Algernon Parsons|Parsons]] alleviated this problem by his suggestion of fitting more powerful astern turbines on all four shafts, which could increase manoeuvrability by reversing the turbines as needed.<ref>Roberts, pp. 68–69</ref>

An additional solution was to fit twin balanced rudders behind each inner shaft, in contrast to the single central rudder used on earlier ships. This greatly increased the effectiveness of the rudder and substantially decreased the turning circle of the ''Invincible''s in comparison to earlier ships of their size.<ref>Roberts, pp. 69–70</ref>

The ''Invincible''s had two paired sets of Parsons turbines housed in separate engine-rooms. Each set consisted of a high-pressure ahead and astern turbine driving an outboard shaft, and a low-pressure ahead and astern turbine driving an inner shaft. A cruising turbine was also coupled to each inner shaft, although these were not used often and were eventually disconnected. Each shaft drove a propeller {{convert|11|ft|m}} in diameter. The turbines were designed to produce a total of {{convert|41000|shp|lk=on}}, but reached nearly {{convert|47000|shp|abbr=on}} during trials in 1908. Designed speed was {{convert|25|kn|1}}, but all three bettered {{convert|26|kn|1}} during trials.<ref>Roberts, pp. 76, 80</ref> {{HMS|Indomitable|1907|2}} maintained an average speed of {{convert|25.3|kn|1}} for three days during a passage of the [[Atlantic Ocean|North Atlantic]] in August 1908.<ref>Roberts, p. 75</ref>

The steam plant consisted of 31 [[Yarrow Shipbuilders|Yarrow]] (''Invincible'' and ''Inflexible'') or [[Babcock & Wilcox]] (''Indomitable'') [[water-tube boiler|large-tube boiler]]s, arranged in four boiler rooms.<ref>Roberts, pp. 70–75</ref> Maximum bunkerage was approximately {{convert|3000|LT|MT|-1}} of coal, with an additional {{convert|725|LT|MT}} of [[fuel oil]] to be sprayed on the coal to increase its burn rate.<ref>Roberts, p. 76</ref> At full fuel capacity, the ships could steam for {{convert|3090|nmi|lk=in}} at a speed of {{convert|10|kn}}.<ref name=c24>Preston, p. 24</ref>

===Armament===
[[File:HMS Indomitable guns LOC 16724.jpg|thumb|left|The guns of 'P' and 'Q' turrets trained across the deck|alt=The crowded midships area of {{HMS|Indomitable|1907|6}} dominated by the masses of the 12-inch guns of 'P' and 'Q' turrets, each of which is trained across the deck]]
Each carried eight [[BL 12 inch Mk X naval gun|BL 12-inch (305&nbsp;mm) Mk X guns]] in four hydraulically powered BVIII twin [[gun turret|turrets]], except for ''Invincible'' which mounted her guns in two BIX and two BX electrically driven turrets. Two turrets were mounted fore and aft on the centreline, identified as 'A' and 'X' respectively. Two turrets were mounted amidships between the second and third funnels, identified as 'P' and 'Q'. 'P' turret was mounted on the port side and normally faced forward, 'Q' turret was mounted on the starboard side and normally faced aft (rearwards). 'P' and 'Q' turrets were staggered—'P' was forward of 'Q', enabling 'P' to fire in a limited arc to the starboard side and 'Q' to likewise fire in a limited arc towards the port side. These were the same guns as those mounted in the British {{HMS|Dreadnought|1906|6}}, the {{sclass|Lord Nelson|battleship|4}} and the {{sclass|Bellerophon|battleship|4}}, and for a brief period the ''Invincible''s equalled the firepower of any other nations' battleships.<ref>Roberts, pp. 81–84</ref>

The guns could initially be depressed to −3° and elevated to 13.5°, although the turrets were modified to allow 16° of elevation during [[World War I]]. They fired {{convert|850|lb|kg|adj=on}} projectiles at a [[muzzle velocity]] of {{convert|2725|ft/s|m/s|abbr=on}}; at 13.5°, this provided a maximum range of {{convert|16450|m|yd|abbr=on}} with [[Armor-piercing shot and shell|armour-piercing (AP)]] 2 [[List of British ordnance terms#C.R.H.|crh]] shells. At 16° elevation, the range was extended to {{convert|20435|yd|m|abbr=on}} using the more aerodynamic, but slightly heavier 4 crh AP shells. The rate of fire of these guns was 1–2 rounds per minute.<ref>{{cite web|url=http://www.navweaps.com/Weapons/WNBR_12-45_mk10.htm|title=Britain 12"/45 (30.5&nbsp;cm) Mark X |date=30 January 2009|access-date=13 October 2009}}</ref> The ships had a total of 880 rounds during wartime for 110 shells per gun.<ref name=r3>Roberts, p. 83</ref>

The ships' [[secondary armament]] initially was intended to consist of eighteen {{convert|3|in|adj=on}} [[QF 12 pounder 12 cwt naval gun|12-pdr]] guns, but firing trials against the old destroyer {{HMS|Skate|1895|2}} in 1906 showed that the 12-pdr gun had little chance of stopping a destroyer or torpedo boat before it got close enough to fire its torpedoes.

[[File:Inflexible Q turret 4 inch gun.jpg|thumb|right|{{center|4-inch guns seen mounted on roof of ''Inflexible'''s Q turret, 1909}}]]
The originally intended 12-pounder guns were exchanged for sixteen [[QF 4 inch naval gun Mk I - III|4-in (102&nbsp;mm) QF Mk III guns]] early in the construction process. They were positioned in the superstructure and on turret roofs in open mounts as they were not expected to be manned in a ship-to-ship engagement during daylight. During 1914–15 the turret roof guns were transferred to the superstructure and the total number of guns was reduced to twelve. All of the remaining guns were enclosed in [[casemate]]s and given blast shields at that time to better protect the gun crews from weather and enemy action.<ref>Roberts, pp. 96–97</ref>

The guns on their PI* mounts had a maximum depression of 10° and a maximum elevation of 20°. They fired {{convert|25|lb|kg|adj=on}} projectiles at a muzzle velocity of {{convert|2300|-|2370|ft/s|m/s|abbr=on}}; at 20°, this provided a maximum range of {{convert|9600|yd|m|abbr=on}} using [[British ordnance terms#Common Pointed|Common pointed]] shells. Their rate of fire was 8–10 rounds per minute.<ref>{{cite web|url=http://www.navweaps.com/Weapons/WNBR_4-40_mk3.htm|title=British 4"/40 (10.2&nbsp;cm) QF Marks I, II and III |date=10 January 2009|access-date=13 October 2009}}</ref>

These guns were replaced by twelve [[BL 4 inch Mk IX naval gun|4-inch BL MK IX]] guns on CPI mountings on ''Inflexible'' during 1917.<ref name=r3/> They could depress 10° and elevate to 30°. They fired {{convert|31|lb|kg|adj=on}} shells at a muzzle velocity of {{convert|2625|ft/s|m/s|abbr=on}} to a maximum range of {{convert|13500|yd|m|abbr=on}} at a rate of fire of 10–12 rounds per minute.<ref>{{cite web|url=http://www.navweaps.com/Weapons/WNBR_4-45_mk9.htm|title=Britain 4"/45 (10.2&nbsp;cm) BL Marks IX and X|date=28 February 2009|access-date=15 October 2009|archive-url=https://web.archive.org/web/20120217005213/http://navweaps.com/Weapons/WNBR_4-45_mk9.htm|archive-date=17 February 2012|url-status=dead}}</ref>

The QF Mk III guns were replaced by twelve [[BL 4 inch naval gun Mk VII|4-inch BL MK VII]] guns on PVI mountings on ''Indomitable'' during 1917.<ref name=r3/> These guns could depress 7° and elevate to 15°. They fired {{convert|31|lb|kg|adj=on}} shells at a muzzle velocity of {{convert|2864|ft/s|m/s|abbr=on}} which gave a maximum range of {{convert|11600|yd|m|abbr=on}}. Their rate of fire was 6–8 rounds per minute. An additional gun was fitted on ''Indomitable'' in April 1917 as an [[Anti-aircraft warfare|anti-aircraft]] (AA) gun. It was mounted on a MK II high-angle mounting with a maximum elevation of 60°. It had a reduced propellant charge with a muzzle velocity of only {{convert|2864|ft/s|m/s|abbr=on}}.<ref>{{cite web|url=http://www.navweaps.com/Weapons/WNBR_4-50_mk7.htm|title=BL 4-inch naval gun Mk VII|access-date=15 October 2009}}</ref>

Earlier anti-aircraft guns included a 3-pounder [[Hotchkiss gun]] on a high-angle Mk Ic mounting with a maximum elevation of 60°. Both ''Invincible'' and ''Indomitable'' carried theirs from November 1914 to August 1917.<ref name=r3/> It fired {{convert|3.3|lb|kg|adj=on}} projectiles at a muzzle velocity of {{convert|1873|ft/s|m/s|abbr=on}} at a rate of fire of 20 rounds per minute. This provided a maximum range of {{convert|7600|yd|m|abbr=on}} at 45°, but the maximum effective anti-aircraft range was only {{convert|1200|yd|m|abbr=on}}.<ref>{{cite web|url=http://www.navweaps.com/Weapons/WNBR_3pounder_H_mk1.htm|title=British Hotchkiss 3-pdr (1.4&nbsp;kg) [1.85"/40 (47 mm)] QF Marks I and II|date=27 February 2007|access-date=15 October 2009}}</ref>

Each of the ''Invincible''s was also fitted with a single [[QF 3-inch 20 cwt]] AA gun on a high-angle MKII mount at the aft end of the superstructure.<ref name=r3/> This had a maximum depression of 10° and a maximum elevation of 90°. It fired a {{convert|12.5|lb|kg|adj=on}} shell at a muzzle velocity of {{convert|2500|ft/s|m/s|abbr=on}} at a rate of fire of 12–14 rounds per minute. They had a maximum effective ceiling of {{convert|23500|ft|m|abbr=on}}.<ref>{{cite web|url=http://www.navweaps.com/Weapons/WNBR_3-45_mk1.htm|title=British 12-pdr [3"/45 (76.2 cm)] 20cwt QF HA Marks I, II, III and IV |date=27 February 2007|access-date=15 October 2009}}</ref>

Gardiner and Gray quote an additional seven [[Maxim gun]]s, but this cannot be confirmed. Five [[British 18 inch torpedo|18-inch (450&nbsp;mm)]] submerged [[torpedo tube]]s were mounted on the ''Invincible''s, two on each side and one in the stern<ref name=c24/> and fourteen torpedoes were carried.<ref name=r3/>

===Fire control===
The spotting tops at the head of the fore and main masts controlled the fire of the ''Invincible''s' main guns. Data from a {{convert|9|ft|m|adj=on|1}} [[Barr and Stroud]] [[Rangefinding telemeter|rangefinder]] was input into a [[Dumaresq]] mechanical computer and electrically transmitted to [[Vickers range clock]]s located in the Transmitting Station located beneath each spotting top where it was converted into range and deflection data for use by the guns. The target's data was also graphically recorded on a plotting table to assist the gunnery officer in predicting the movement of the target. Each gun turret had its own transmission equipment and the turrets, Transmitting Stations, and spotting tops could be connected in almost any combination. Firing trials against {{HMS|Hero|1885|2}} in 1907 revealed this system's vulnerability to gunfire as the spotting top was hit twice and a large splinter severed the [[Speaking tube|voice pipe]] and all wiring running along the mast. To guard against this possibility, 'A' turret was fitted, during refits between 1911 and 1914, with a 9-foot rangefinder at the rear of the turret roof and it was equipped to control the entire main armament.<ref>Roberts, pp. 90–91</ref>

Fire control technology advanced quickly during the years immediately preceding World War I and the development of the [[Frederic Charles Dreyer#Dreyer Fire Control Table|Dreyer Fire Control Table]] was one such advance. It combined the functions of the Dumaresq and the range clock and a simplified version, the Mk I, was fitted to the ''Invincible''s during refits in 1915–16. The more important development was the director firing system. This consisted of a [[Fire-control system#Naval fire control|fire control director]] mounted high in the ship which electrically provided gun data to the turrets via pointers, which the turret crewmen only had to follow. The director officer fired the guns simultaneously, which aided in spotting the shell splashes and minimised the effects of the roll on the dispersion of the shells. ''Invincible'' was the first battlecruiser to receive this system during her refit from April to August 1914, but its installation was interrupted by the outbreak of the war and it was not fully working until after the [[Battle of the Falkland Islands]] in November. ''Indomitable'' and ''Inflexible'' didn't receive their systems until May 1916, immediately before the [[Battle of Jutland]].<ref>Roberts, pp. 92–93</ref>

===Protection===
The armour protection given to the ''Invincible''s the waterline [[Belt armor|belt]] measured {{convert|6|in|mm|0}} amidships was only slightly more than half the thickness of {{HMS|Dreadnought|1906|2}}'s {{convert|11|in|mm|0}}. The belt was six inches thick roughly between the fore and aft twelve-inch gun turrets, but was reduced to four inches from the fore turret to the bow and did not extend aft of the rear turret. A six-inch [[bulkhead (partition)|bulkhead]] met the [[barbette]] of X turret to fully enclose the armoured citadel. The gun turrets and barbettes were protected by {{convert|7|in|mm|0|abbr=on}} of armour, except for the turret roofs which used {{convert|3|in|mm|0|abbr=on}} of [[Krupp]] non-cemented armour (KNC). The thickness of the main [[deck (ship)|deck]] was {{convert|1|in|mm|0|abbr=on}} around the base of barbettes and the crown of the base of the rear [[conning tower]]. It was {{convert|2|in|mm|0|abbr=on}} over the crown of the base of the forward conning tower. The lower deck armour was {{convert|1.5|in|mm|0|abbr=on}} on the flat and two inches thick on the slope, except aft of the rear turret where it was increased to {{convert|2.5|in|mm|0|abbr=on}} to protect the steering gear. The front and sides of the forward conning tower were {{convert|10|in|mm|0|abbr=on}} thick while its rear was {{convert|7|in|mm|0|abbr=on}}. The walls of the rear conning tower were six inches thick. The roof and floor of both conning towers were KNC armour 2&nbsp;inches thick while their communication tubes were {{convert|3|in|mm|0|abbr=on}} of KNC. The signal tower immediately aft of the forward conning tower also had three inches of KNC. [[Plain-carbon steel|Mild steel]] [[torpedo bulkhead]]s of 2.5-inch thickness were fitted abreast the [[magazine (artillery)|magazine]]s and shell rooms. [[Krupp cemented armour]] was used throughout, unless otherwise mentioned.<ref>Roberts, pp. 109, 112</ref>

===Aircraft===
By 1918 the two surviving ''Invincible''s carried a [[Sopwith Pup]] and a [[Sopwith 1½ Strutter]] on flying-off ramps fitted on top of 'P' and 'Q' turrets.<ref name=c24/> Each platform had a canvas hangar to protect the aircraft during inclement weather.<ref>Roberts, p. 92</ref>