of 15°. They fired projectiles at a muzzle velocity of ; this gave a maximum range of . Their rate of fire was 6–8 rounds per minute. They were provided with 100 rounds per gun. 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 . 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 1914–15. 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 . It was provided with 500 rounds. New Zealand carried a single QF 6 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. It had a maximum ceiling of , but an effective range of only . They mounted two 17.7-inch (450-mm) submerged torpedo tubes, one on each side aft of 'X' barbette, for which twelve torpedoes were carried. 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