“Rigging for red” means using dim red lighting to preserve night vision (or “dark adaptation”).
Red lighting has frequently been used on submarines since World War II.
Nowadays, it’s much less common to see dark red lighting on subs, as scientific research has shown that human vision may respond better with dimmable white, green or even blue light instead.
https://joyinliberty.com/qanon/rig-for-red/
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