 Short @-@ range air defence was provided by 73 Bofors 40 mm AA guns in a variety of mountings . Vanguard had ten sextuple @-@ barrel power @-@ operated mounts concentrated in the superstructure and stern , a twin @-@ barrel mount on ' B ' turret , and 11 power @-@ operated single mounts on the upper deck and rear superstructure . All mounts could depress to − 10 ° and elevate to a maximum of + 90 ° . The 40 @-@ millimetre ( 1 @.@ 6 in ) gun fired a 1 @.@ 97 @-@ pound ( 0 @.@ 89 kg ) shell at a muzzle velocity of 2 @,@ 890 ft / s ( 880 m / s ) to a distance of 10 @,@ 750 yards ( 9 @,@ 830 m ) . The gun 's rate of fire was approximately 120 rounds per minute . Space was not available to stow the standard allowance of 1564 rounds per gun , and Vanguard only carried 1269 rounds per gun . Two of the single guns on the quarterdeck were removed in 1949 and five others during a major refit in 1954 . All of her multiple Bofors mounts were removed at this same time . 
