How fleet size turns ships into available capability

Why do two carriers fail to guarantee one at sea, and how many ships are needed for dependable availability?

Under the stated rule of thumb, two usually make one available, three usually provide one at sea, and four support continuous deployment, with larger fleets supplying more available ships.

Two carriers cannot always ensure one is available because defects, refits, and salt-water maintenance do not follow a neat alternating schedule. The planning rule of thumb distinguishes possession from capability: one ship is intermittent, two usually make one available, three usually put one at sea, and four guarantee continuous deployment within this model. Five provide one at sea plus another available, while six provide two at sea. The four-ship example is the ballistic-missile submarine force. The same approach is applied to the U.S. requirement for eleven operational carriers and an expected four available. These are availability estimates that account for maintenance and readiness cycles.