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Commonly called "Chinese underwear" and seen used mainly by maintenance personnel, although I've heard the guys in the back of AC-130s wore them under their flightsuits. I have some 1970s versions that I put in the car for emergencies, use to walk the dog, and even keep one at the office if I get cold at my desk. Not very stylish, but warm and comfortable when you need it.
Also have some issued when I deployed to Alaska.