Editing Invincible-class battlecruiser (section)

===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/>