SM-3 is a dedicated ballistic-missile defence weapon with greater reach in that role. SM-6 is an area air-defence missile with more limited ballistic-missile defence capability. More ships are likely to carry SM-6, making it more likely to be available when needed. Adding that secondary capability also raises cost. SM-2 does not meet the ballistic-missile defence requirement.
Notable Point · 55:57-56:58
SM-3, SM-6 and ballistic missile defence
Dedicated ballistic-missile defence differs from a secondary interception capability in an air-defence weapon.