Jeffery Williams, an officer in the Canadian Army, wrote a history of the Northwest European campaign from the end of Normandy to VE-Day ("The Long Left Flank"). He mentioned that everybody was cold in the winter of 1944-45, but it seemed to him that the Americans "looked colder" than everyone else.....
I believe that they were indeed colder than everyone else. As part of no particular coordinated effort, through the years I have purchased and wear several items of WWII US Army winter gear, which I mix in with my wardrobe, to include: Model 1941 Field Jacket, Tanker Jacket, wool 6 button pull over sweater, and even a B-10 Flight jacket.
The M41 field jacket is little better than a windbreaker, and I cannot imagine going anyplace below zero in it. It simply is not winter wear, suitable only for fall and spring.
The Tanker Jacket is better, with a thicker wool lining, knit cuffs & collar, and a banded bottom. However it is short and pales next to an actual parka.
The B-10 flight jacket is probably the warmest of the three with the nice shearling collar, but again it is short
(purposely so, to provide freedom of movement in a cockpit).
And then there's the GI sweater (
which in my experience is a make or break item in true cold). It is of a fairly loose weave and short - and consequently feels a bit "insubstantial" for a wool sweater.
I'm sure if I tried to survive a winter in Belgium
(or up in your Calgary area) with this gear I would be truly miserable.
My guess is the Mackinaw would be the winner in a Warmth Popularity Contest.
Edit: I apologize for the size of the images, they are not nearly that big on my computer, I don't know why they seem to fill the screen in this post.