As long as you're moving you're fine - assuming your clothes are not totally absurdly inadequate for the weather.

The trouble is that when you stop it is virtually impossible to keep warm without external heat (fire) or insulation (sleeping bag). If you're wet or damp you chill faster. Wearing wool pushes the envelope, but does not reverse the laws of physics: If you're dressed for moving you WILL be cold when you stop. Just rest long enough and you start to chill.

I have never tried sloshing through mud for 12 hours, but I guess I would be pretty hard pressed for a little rest & rehydration, eating about half a cow and sleeping 16 hours. OK, I guess I COULD manage without the two lasts items if I really had to, but not rest & rehydration. Those are not optional items.