Rig for red... "Rig for Red" is normally a command used in the Control Room. It is normally used when the boat is going to be surfacing or coming to Periscope Depth at night. The purpose is to give the lookouts and the officer designated to head to the bridge upon surfacing a chance for their eyes to adjust to darkness, or the OOD the same thing before looking through the Periscope.  https://www.answers.com/Q/What_does_it_mean_to_Rig_For_Red_and_what_is_is_used_for