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.

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.

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.

These were to be based in Australia, New Zealand, Canada and South Africa in 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.

[2] Australia became a ship of the newly formed Royal Australian Navy, while New Zealand was retained in European waters as a wholly RN unit.

They fired 850-pound (390 kg) projectiles at a muzzle velocity of 2,725 ft/s (831 m/s); at 13.5°, this provided a maximum range of 16,450 m (17,990 yd) with armour-piercing (AP) 2 crh shells.

[17] New Zealand carried a single QF 6 pounder Hotchkiss AA gun on a HA MkIc mounting from October 1914 to the end of 1915.

Firing trials against Hero 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.

[4][35] Indefatigable, accompanied by Indomitable, under the command of Admiral Sir Archibald Berkeley Milne, encountered the German battlecruiser Goeben and the light cruiser Breslau on the morning of 4 August 1914 headed east after a cursory bombardment of the French Algerian port of Philippeville, but Britain and Germany were not yet at war so Milne turned to shadow the Germans as they headed back to Messina to recoal.

Milne therefore stationed Inflexible and Indefatigable at the northern exit of the Straits of Messina, still expecting the Germans to break out to the west where they could attack French troop transports; he stationed the light cruiser Gloucester at the southern exit and sent Indomitable to recoal at Bizerte, where she was better positioned to react to a German sortie into the Western Mediterranean.

Milne, still expecting Rear Admiral Wilhelm Souchon to turn west, kept the battlecruisers at Malta until shortly after midnight on 8 August, when he set sail for Cape Matapan, where Goeben had been spotted eight hours earlier, at a leisurely 12 knots (22 km/h; 14 mph).

In a twenty-minute bombardment, a single shell struck the magazine of the fort at Sedd el Bahr at the tip of the Gallipoli peninsula, displacing (but not destroying) 10 guns and killing 86 Turkish soldiers.

[39] Following the declaration of war, Australia was assigned to find the German East Asia Squadron, the only Central Powers naval force of note in the Pacific.

[43] New Zealand's first action was as part of the battlecruiser force under the command of Admiral Beatty during the Battle of Heligoland Bight operation on 28 August 1914.

They turned south at full speed at 11:35 AM when the British light forces failed to disengage on schedule and the rising tide meant that German capital ships would be able to clear the bar at the mouth of the Jade estuary.

An earlier Raid on Yarmouth on 3 November had been partially successful, but a larger-scale operation was devised by Admiral Franz von Hipper afterwards.

The fast battlecruisers would actually conduct the bombardment while the entire High Seas Fleet was to station itself east of Dogger Bank to provide cover for their return and to destroy any elements of the Royal Navy that responded to the raid.

Vice Admiral Sir George Warrender, commanding the 2nd Battle Squadron, had received a signal at 05:40 that Lynx was engaging enemy destroyers although Beatty had not.

This started a fire amidships that destroyed her two port 21 cm (8.3 in) turrets and the concussion damaged her engines so that her speed had dropped to 17 knots (31 km/h; 20 mph) and her steering gear jammed.

Almost immediately afterwards, at 15:32, he ordered a course change to east south-east to position himself astride the German's line of retreat and called his ships' crews to action stations.

Hipper ordered his ships to turn to starboard, away from the British, to assume a south-easterly course, and reduced speed to 18 knots (33 km/h; 21 mph) to allow three light cruisers of the 2nd Scouting Group to catch up.

[51] This began what was to be called the 'Run to the South' as Beatty changed course to steer east south-east at 3:45, paralleling Hipper's course, now that the range closed to under 18,000 yards (16,000 m).

Around 16:00 Indefatigable was hit by two or three shells from Von der Tann around the rear turret and almost immediately fell off to starboard and was down by the stern and listing to port.

[55] At 16:30 the light cruiser Southampton, scouting in front of Beatty's ships, spotted the lead elements of the High Seas Fleet charging north at top speed.

[57] Beatty's ships maintained full speed to try to put some separation between them and the High Seas Fleet and gradually moved out of range.

By 18:35 Beatty was following Indomitable and Inflexible of the 3rd BCS as they were steering east-southeast, leading the Grand Fleet, and continuing to engage Hipper's battlecruisers to their southwest.

[64] Australia rejoined the 2nd BCS on 9 June 1916 as the squadron flagship, but there was little significant naval activity for the Indefatigables, other than routine patrolling, thanks to the Kaiser's order that his ships should not be allowed to go to sea unless assured of victory.

New Zealand was refitted between December 1918 and February 1919 for Admiral Jellicoe's year-long tour of India and the Dominions and she was paid off upon her return on 15 March 1920 into reserve.