 The ship 's main armament consisted of eight 42 @-@ calibre BL 15 @-@ inch Mk I guns in four twin hydraulically powered gun turrets designated ' A ' , ' B ' , ' X ' and ' Y ' from bow to stern . When the turrets were modernised their maximum elevation was increased to + 30 ° , although the guns were loaded at + 5 ° . They fired 1 @,@ 938 @-@ pound ( 879 kg ) projectiles at a muzzle velocity of 2 @,@ 458 ft / s ( 749 m / s ) ; this provided a maximum range of 33 @,@ 550 yards ( 30 @,@ 680 m ) . These guns were also capable of firing the same projectiles while using supercharges which gave a maximum range of 37 @,@ 870 yards ( 34 @,@ 630 m ) . Their rate of fire was two rounds per minute . Vanguard carried 100 shells per gun . 
