Why availability rules apply beyond ships

Do the rules of three and four also apply to aircraft and tanks?

Broadly yes, because training, maintenance, and unpredictable operational demand affect all military equipment, though the exact model must match the asset.

The underlying issue is the cycle through operations, training, repair, and deep maintenance. Models developed for lorry fleets can understate military risk because commercial vehicles are easily hired and rarely face sudden crisis surges comparable to a carrier. Availability calculations must therefore reflect the actual platform and mission rather than merely reuse a convenient civilian model.