Eighteen fighters as a minimum sustained patrol group

Why treat eighteen fighters as the minimum combat-air-patrol group in a three-dimensional environment?

Eighteen supports a modest continuous patrol and alert cycle; full multi-axis defense would require a larger carrier-style air group.

The figure of eighteen aircraft comes from carrier experience in the Pacific and Korea, as well as the Invincible-class air group. That number can sustain two pairs on station and another two on alert, providing warning and strike dilution rather than airtight control of every axis. Space adds approach directions, but it also lets both the patrols and their parent ship maneuver in three dimensions. A larger group of thirty-two aircraft could keep about eight deployed and another eight ready, allowing more axes to be watched. Expanding the group much further would change the vessel from a battlecruiser into a carrier.