Former Subanon here,
Rigging for red is typically done in the control room for periscope depth at night or surfacing at night. It’s not needed as much anymore due to the optics in periscopes these days.
Silent running is also something that is a bit outdated but still relevant. Any non-essential operations are ceased. Our modern subs are damn near silent already 😉. Usually it is done when you are getting into close proximity of the enemy and preparing for an attack. It would also be done to sneak away or into somewhere for operations or avoiding detection in the event of depth charges. Just some info for you