How many ships sustain a force at sea?

How large must a class be to keep five ships continuously at sea?

About twelve can usually sustain five deployed ships, while fifteen gives a more dependable margin for maintenance and disruption.

The familiar one-in-three ideal is a planning guide rather than a rigid law. Ten ships might sustain five deployed hulls under strain, but the margin would be fragile. Twelve should usually keep five at sea through ordinary maintenance cycles. Fifteen makes the same commitment much more dependable when refits, repairs, and unforeseen work intervene. A headline fleet total must be translated into readiness and force generation.