 The secondary armament consisted of sixteen 50 @-@ calibre QF 5 @.@ 25 @-@ inch Mk I * dual purpose guns in eight twin gun mounts . They had a maximum depression of − 5 ° and a maximum elevation of 70 ° . They fired an 80 @-@ pound ( 36 kg ) high @-@ explosive shell at a muzzle velocity of 2 @,@ 672 ft / s ( 814 m / s ) . The improved 5 @.@ 25 turrets on Vanguard were claimed to be fully automatic , with a power @-@ rammed breech and automatic tracking and elevation under radar control enabling a rate of fire was about 18 rounds per minute . At maximum elevation , the guns had a maximum range of 24 @,@ 070 yards ( 22 @,@ 010 m ) . 391 rounds were provided for each gun . 
