Better missile defense raises the cost of attack

What happens when missile defense becomes markedly better?

Attackers must fire more weapons to preserve their chance of hitting, raising the cost and logistical burden of every strike.

More effective missile defence increases the number of attacking missiles needed for a comparable chance of a hit. The same target therefore demands a larger expenditure of weapons. That raises the cost of an intervention without making a defended ship invulnerable. The relationship is qualitative, with no numerical interception rate or required salvo size calculated here.