Do yourself a favor and get the "optional" all-weather coat, or what I would've called a short overcoat in the service. It's a reasonable weight that packs down, falls to around the knee, has a zip out Thinsulate liner, and repels water. It'll keep you warm for most of the winter, and without the liner makes a fine raincoat the rest of the year.

That issue trench coat must've been designed by someone who never wears a trench. That said, it'll keep you warm for the couple of days when it gets really cold at ORD. Pairs nicely with DSCP's finest issue leather dress gloves if you still have those.

On a side note, the ORD ramp gets slushy and wet with deice during the winter. I found that ankle boots, like chukka type, paid dividends in keeping water off of socks. Low quarters don't cut it then.