The Indefatigable class were the second class built of British battlecruisersThe Indefatigable-class ships were formally known as armoured cruisers until 1911 when they were redesignated as battlecruisers by an Admiralty order of 24 November 1911. Unofficially a number of designations were used until then, including cruiser-battleship, dreadnought cruiser and battle-cruiser. See Roberts, pp. 24–25 which served in the Royal Navy and the Royal Australian Navy during World War I. The design represented a modest reworking of the preceding , featuring increased endurance and an improved cross-deck arc of fire for their midships wing turrets achieved by a lengthening of the hull. Like its predecessor, the design resembled the contemporary dreadnought of the Royal Navy, but sacrificed armour protection and one turret from the main battery for a speed advantage.
Originally was the only ship of the class, but and were later built as part of a scheme to improve the defence of the Dominions by having each Dominion purchase a "fleet unit" of one battlecruiser, three light cruisers and six destroyers. Only Australia fully acceded to the idea, forming the Royal Australian Navy, but New Zealand agreed to fund one battlecruiser. A modified Indefatigable design was chosen rather than the then building for the Royal Navy.
They spent most of the war patrolling the North Sea, and participated in most of the battles there, although only New Zealand was in the United Kingdom when the war began. Indefatigable was in the Mediterranean where she pursued the German warships and as they fled toward Turkey, and Australia was flagship of the Royal Australian Navy in Australian waters where she helped to secure the German Pacific colonies and searched, unsuccessfully, for the German East Asia Squadron before sailing for the United Kingdom in December 1914. New Zealand participated in a number of the early actions in the North Sea including the Battle of Heligoland Bight and the inconclusive Scarborough Raid. Australia was still under repair after a collision with New Zealand before the Battle of Jutland so only Indefatigable and New Zealand were present when the former was destroyed by a magazine explosion. Both Australia and New Zealand spent much uneventful time at sea after Jutland waiting for the next appearance of the High Seas Fleet, but that had been forbidden by the Kaiser. New Zealand conducted Admiral Jellicoe on his tour of India and the Dominions after the war while Australia returned home where she again became the flagship of the Royal Australian Navy. New Zealand was sold for scrap in 1922, while Australia lasted only two years more before being scuttled to comply with the terms of the Washington Naval Treaty.
Background Indefatigable was the successor to the Invincible-class battlecruisers. A number of options for large cruisers were considered for the 1906 Naval Programme, including the X4 design of with armour and speed, but in the end this programme consisted only of three ships of the type. A number of options were considered for the 1907–08 programme, ranging from to , but in the end battleships were again favoured and no battlecruisers were ordered until the subsequent programme year.Roberts, pp. 28–29
At the time the final design of Indefatigable was approved, the Admiralty was already moving on, Fisher writing in September 1908 "I've got Sir Philip Watts into a new Indomitable that will make your mouth water when you see it", a design that was to eventually emerge as . In August 1909 the self-governing dominions met at the 1909 Imperial Conference, and in discussion of Imperial defence, the Admiralty proposed the creation of indigenous fleet units, each to consist of one Invincible-class battlecruiser, three light cruisers of the Bristol class, and six destroyers. These were to be based in Australia, New Zealand, Canada and South Africa in an attempt to secure the naval defence of the Dominions while the Royal Navy concentrated in home waters to meet the German threat. While the scheme was rejected by Canada and South Africa, Australia and New Zealand subscribed, each ordering a modified version of the Indefatigable, rather than the originally proposed Invincible class.Lambert, pp. 64–67 Australia became a ship of the newly formed Royal Australian Navy, while New Zealand was retained in European waters as a wholly RN unit.Roberts, p. 29 Eventually, only one fleet unit was formed, the Australian squadron in 1913.
Design
The was ordered as the lone battlecruiser of the 1908–9 programme. Her outline design was prepared in March 1908, and the final design was approved in November 1908. This design was essentially an enlarged with revised arrangements of protection and main armament.Roberts, p. 28
General characteristics The Indefatigables were slightly larger than their predecessors of the . They had an overall length of , a beam of , and a draught of at deep load. The ships displaced at load and at deep load, over more than the earlier ships. They had a metacentric height of at deep load.Roberts, pp. 43–44
Propulsion Each paired set of Parsons direct-drive steam turbines was housed in a separate engine-room and drove two shafts. The wing shaft was coupled to the high-pressure ahead and astern turbines and the low-pressure turbines to the inner shafts. Each wing shaft drove a propeller in diameter and the propellers on the inner shafts were in diameter. The turbines were powered by thirty-one Babcock & Wilcox water-tube boilers in five boiler rooms.Roberts, pp. 70–75 Indefatigables turbines were designed to produce a total of , but reached over on forced draught during trials in 1911. The turbines of Australia and New Zealand were slightly more powerful at . They were designed for , but all three bettered during trials.Roberts, pp. 76, 80
The ships carried approximately of coal, and an additional of fuel oil that was sprayed on the coal to increase its burn rate.Roberts, p. 76 At full capacity, the ships could steam for at a speed of .Preston, p. 26
Armament
Each ship carried eight BL Mk X guns in four BVIII or BVIII* twin-gun turrets. Two turrets were mounted fore and aft of the superstructure on the centreline, identified as 'A' and 'X' respectively. Two wing turrets were mounted amidships en echelon between the 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 70° arc to the starboard side and 'Q' to likewise fire towards the port side. These were the same guns as those mounted in , the and .Roberts, pp. 81–84
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 projectiles at a muzzle velocity of ; at 13.5°, this provided a maximum range of using 4crh shells. The rate of fire of these guns was about two rounds per minute.Friedman 2011, p. 59–61 The ships carried a total of 880 rounds during wartime for 110 shells per gun.Roberts, p. 83
The secondary armament consisted of sixteen BL Mk VII guns positioned in the superstructure. All of the guns were enclosed in casemates and given gun shields during refits in 1914 and 1915 to better protect the gun crews from weather and enemy action, although two guns were removed at the same time.Roberts, p. 97 The guns on their PII* mounts had a maximum depression of 7° and a maximum elevation of 15°. They fired projectiles at a muzzle velocity of ; this gave a maximum range of .Friedman 2011, pp. 97–98 They were provided with 100 rounds per gun.Campbell 1978, p. 13
An additional 4-inch gun was fitted in the surviving ships during 1917 as an anti-aircraft (AA) gun. It was mounted on a Mark II high-angle mounting with a maximum elevation of 60°. It had a reduced propellant charge with a muzzle velocity of only .Friedman 2011, p. 98 Earlier anti-aircraft guns included a single QF 20 cwt AA gun on a high-angle Mark II mount that was added during refits in 1914–1915. This had a maximum depression of 10° and a maximum elevation of 90°. It fired a shell at a muzzle velocity of at a rate of fire of 12–14 rounds per minute. They had a maximum effective ceiling of .Friedman 2014, p. 388 It was provided with 500 rounds. New Zealand carried a single QF six-pounder () Hotchkiss AA gun on a HA MkIc mounting from October 1914 to the end of 1915. This had a maximum depression of 8° and a maximum elevation of 60°. It fired a shell at a muzzle velocity of at a rate of fire of 20 rounds per minute against surface targets. It had a maximum ceiling of .Friedman 2014, p. 387
The battlecruisers were also equipped with two 18-inch (450 mm) submerged torpedo tubes, one on each side of the forward hull, for which twelve torpedoes were carried.Cosentino & Stanglini, p. 97
Fire control
The spotting tops, a modern equivalent of the sailing ship's fighting top, at the head of the tripod fore and main masts controlled the fire of the Indefatigables main guns. Data from a Barr and Stroud rangefinder was input into a Dumaresq mechanical computer and electrically transmitted to Vickers range clocks located in the Transmitting Station (TS) 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 in 1907 revealed this system's vulnerability to gunfire as the spotting top was hit twice and a large splinter severed the voice pipe and all wiring running along the mast. To guard against this possibility 'A' turret of Indefatigable was fitted with a 9-foot rangefinder at the rear of the turret roof and it was equipped to control the entire main armament during a refit between 1911 and 1914.Roberts, pp. 90–91
Australia and New Zealand were built with a different arrangement. The spotting top on the main mast was deleted and an armoured spotting tower was built instead into the conning tower where it was better protected, had an improved field of vision and direct access to the primary conning position. The rear Transmitting Station was also deleted and the forward TS was consequently enlarged. Their 'A' turrets were built with the improvements listed above.Roberts, p. 91
Fire control technology advanced quickly during the years immediately preceding World War I and the development of the 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 Indefatigables during refits in 1915–1916. The more important development was the director firing system. This consisted of a fire-control director mounted high in the ship which electrically transmitted training and elevation angles to the gun turrets via pointers, which the turret crewmen had only to follow. The director layer's trigger fired the guns simultaneously which aided in spotting the shell splashes and minimized the effects of the roll on the dispersion of the shells. A gun within the 'Y' turret was also equipped with transmitters so that, as a backup, it could function as a "directing gun",The Director Firing Handbook, 1917. pp. 88, 142. but there was no provision for the gun battery to be split between the main director and this directing gun.The Director Firing Handbook, 1917. p. 88. The Indefatigables received their director equipment between mid-1915 and May 1916.Roberts, pp. 92–93
Armour