 Their secondary armament consisted of sixteen BL 4 @-@ inch Mark VII guns , most of which were mounted in casemates . The guns on their PII * or PIV * mounts had a maximum elevation of 15 ° . They fired 31 @-@ pound ( 14 @.@ 1 kg ) projectiles at a muzzle velocity of 2 @,@ 864 ft / s ( 873 m / s ) ; this gave a maximum range of 11 @,@ 600 yd ( 10 @,@ 607 m ) . Their rate of fire was 6 – 8 rounds per minute . They were provided with 150 rounds per gun . 
