The Olive Drab Wool Field Jacket in its basic form was designed and classified as a field garment and thus could be worn by both officers and enlisted men. When developed in 1944, it was also authorized to replace the enlisted man's Winter Service Coat in theater of operations.
This example is dated December 16, 1944 and in really nice condition. 
The man it belongs to was in the infantry and finish the war (ruptured duck insignia), the 3 bars on the sleeve represents 18 months of service, is was par of the Third Army, and had two ribbons. The first ribbon is for the American campaign and the second is for the Europe, Africa and Middle East campaign.