The rule of thumb distinguishes a single prestige asset from a force that can be expected to be at sea. One hull is a proof of concept or white elephant, while two offer only intermittent availability and can function mainly as status symbols. Three normally provide a usable capability because one is usually available. Four make the capability dependable despite refits, training cycles, and other absences, revealing whether procurement is serious about sustained operations.
Notable Point · 52:41-53:46
Why four hulls make a dependable naval capability
The familiar one-to-four rule explains why a nominal fleet asset is not necessarily a usable operational capability.