Replacing several hulls with fewer, more capable ships creates an availability risk when standing missions do not shrink with fleet numbers. The rule of thumb offered here is that one ship is a white elephant, two offer only potential, three usually provide a capability, and four can guarantee one available, as with Britain's continuous-at-sea deterrent submarines. Britain once had four principal aviation ships, while a two-carrier fleet can lose the capability when one ship is in refit and the other develops a defect. Paper efficiency cannot substitute for enough hulls to absorb maintenance, training, and accidents. Computer models also struggle to represent crew turnover, dockyard mistakes, and ordinary human disruptions, all of which make a very small fleet more fragile than its idealized availability calculation suggests.
Chapter · 24:31-30:45
Hull numbers determine real availability
A smaller successor class can look efficient on paper while leaving too few ships to cover refits, breakdowns, training, and the fleet's standing missions.