Low vis Nav.
Agree, I got quite adept at navigating wearing a full face oxygen mask! The tube wouldn't reach the sextant mounting tho'
Raising the curtain that cut off light from the nav table, and opening the face level air vent, helped a bit too.
Had a Captain who decided to fly on "red only" light selection once, the switch to activate this mode being in his control, and of course the Loran chart required one to identify coloured lines, some red, which promptly became invisible of course. We had a few words about the ongoing navigation accuracy.
I won.