Melbourne and Sydney illustrate a basic force-structure problem: a single ship is frequently unavailable, while two can usually keep one ready. Three ships make an available capability much more dependable, and four can support a nearly guaranteed commitment. More hulls make readiness resilient because training, transit, refit, and unexpected defects can be spread across the fleet. The same logic applies to the numbers required for a continuously available ballistic-missile-submarine deterrent.
Notable Point · 30:20-33:26
Why fleet numbers determine carrier availability
A two-carrier Australian fleet usually kept one ship available, while larger fleets could absorb maintenance and training without losing the capability altogether.