Why would other navies panic if Britain could mass-produce carriers, battleships, cruisers, and destroyers without normal construction-time or manpower penalties?
Short answerThe same production capability could become available to other countries, while Britain would still need enough crews or extensive automation to operate its new ships.
NotesA technology capable of mass-producing complex warships without normal time constraints would alarm rival powers. If Britain could use it, other countries could use the same capability. Producing hulls would still leave the problem of finding enough people to operate them. Removing that manpower constraint is taken to imply minimal crews and extensive automation.