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. 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. The ships carried approximately of coal, and an additional of fuel oil that was to be sprayed on the coal to increase its burn rate. At full capacity, the ships could steam for at a speed of . Armament Each ship carried eight BL Mk X guns in four BVIII* twin turrets. Two turrets were mounted fore and aft 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 . 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 with armour-piercing (AP) 2 crh shells. At 16° elevation, the range was extended to using the more aerodynamic, but slightly heavier 4 crh AP shells. The rate of fire of these guns was 1–2 rounds per minute. The ships carried a total of 880 rounds during wartime for 110 shells per gun. The secondary armament consisted of sixteen BL Mk VII guns positioned in the superstructure. All of the guns were enclosed in casemates and given blast 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. The guns on their PII* mounts had a maximum depression of 7° and a maximum elevation