How many ships make a class operationally viable?

How many ships are needed for a class to be viable at good operational readiness?

It depends on the mission, but three begins to create usable availability, four can secure one at sea, and larger multiples provide resilience and surge capacity.

The mission determines a viable class size. Two hulls provide only theoretical choice, while three usually make practical availability possible and four improve confidence that one can remain at sea. Five add surge capacity, and larger escort groups scale upward according to how many ships must be deployed and ready to reinforce them. Training, maintenance, and refit account for the hulls absent from the front line at any given moment. The familiar rule of threes and fives is a readiness model, not a slogan about total ship numbers.