Thanks everyone. It makes sense to me now!

Did pilots wear goggles though?
The colour film shot of RAF Bomber Command Lancasters (the one with the white dog) and Memphis Belle both show pilots and crewmen without goggles?
Of course this could have been just for the filming.
At 18’000 feet and -40 degrees I’m amazed the eyes didn’t just freeze solid in those unheated, unpressurised aircraft goggles or not!