Indefatigable-class battlecruiser

Australia in 1914
Class overview
Name	Indefatigable class
Operators	Royal Navy  Royal Australian Navy
Preceded by	Invincible class
Succeeded by	Lion class
Subclasses	New Zealand
Built	1909–1913
In service	1911–1923
In commission	1911–1923
Completed	3
Lost	1
Scrapped	2
General characteristics
Type	Battlecruiser
Displacement	18,500 long tons (18,800 t) (normal) 22,130 long tons (22,490 t) (deep load)
Length	590 ft (179.8 m)
Beam	80 ft (24.4 m)
Draught	27 ft (8.2 m)
Installed power	31 Babcock & Wilcox boilers 43,000 ihp (32,000 kW)
Propulsion	4 shafts; 2 steam turbine sets
Speed	25.8 knots (47.8 km/h; 29.7 mph)
Range	6,690 nmi (12,390 km; 7,700 mi) at 10 knots (19 km/h; 12 mph)
Complement	800
Armament	4 × twin 12 in (305 mm) guns 16 × single 4 in (102 mm) guns 2 × submerged 17.7 in (450 mm) torpedo tubes
Armour	Belt: 4–6 in (102–152 mm) Decks: 1.5–2.5 in (38–64 mm) Barbettes: 7 in (178 mm) Turrets: 7 in (178 mm) Conning tower: 4–10 in (102–254 mm) Torpedo bulkheads: 2.5 in (64 mm)

The Indefatigable class were the second class built of British battlecruisers^{[Note 1]} which served in the Royal Navy and the Royal Australian Navy during World War I. The design represented a modest reworking of the preceding Invincible class, 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 4-knot (7.4 km/h; 4.6 mph) speed advantage.

Originally Indefatigable was the only ship of the class, but Australia and New Zealand 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 Lion-class battlecruiser 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 Goeben and Breslau as they fled towards 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 only lasted two years more before being scuttled to comply with the terms of the Washington Naval Treaty.
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