Very good, but had he got a Phantom course he would have been issued with Lyle and Scott's finest Y-front long johns is cotton or wool nylon.
Sounds very like Australian Army issue John L's - named after the noted bare knuckle prize fighter.
The latter were a masterpiece of design that would shrink in the wash and itched like b*ggery.
Wouldn't know - don't think I ever wore mine. And don't think anybody else I knew did either.