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. 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 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. Australia became a ship of the newly formed Royal Australian Navy, while New Zealand was retained in European waters as a wholly RN unit. 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. 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. They displaced at load and at deep load, over more than the earlier ships. They had a metacentric height of at deep load. 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