Why gunfire and missiles need different measures of air defence

A missile is commonly assessed by the probability that it destroys its target. Anti-aircraft gunfire also sought to disrupt an attack by forcing aircraft to turn away, release weapons early or continue while damaged. Measuring guns only by the missile standard can miss those effects. The reverse comparison does not automatically favour missiles either. This helps explain why some ships retained gun-centred air defence during the transition to missile systems, when designers had to decide which use of limited weight offered the better protection.