This vintage mackinaw was made in the 1940s for a US army officer. It has a shawl collar, is double breasted, and belted. This one has seen a lot of wear, though it’s hard to know whether it was during the war or post-war, as these were popular as surplus as workwear.
Chest (pit to pit): 21″ (doubled = 42″)
Shoulder to shoulder:18″
Sleeve (shoulder to cuff): 25-1/2″