Excerpt from pages 128 to 129 of DA PAM 670–1 • 2 December 2014
20–7. Coats, black, all-weather (male and female)
. The black, all-weather coat is a clothing bag issue item.
. The black, all-weather coat is made of polyester/cotton (65/35) in Army shade 385. The coat is a sixbutton, double-breasted model with a belt, convertible collar that buttons at the neck, gun flap, shoulder loops, adjustable sleeve straps, welt pockets with two inside hanging pockets, and zip-out liner. The back of the coat has a yoke and center vent. The coat is one-quarter lined with basic material; the sleeve lining is made of nylon taffeta (see fig 20–7). There is no wear-out date for the interim version of the double-breasted coat made from polyester/cotton (50/50).
Figure 20–7. Army black all-weather coat with officer insignia
c. How worn
. Personnel may wear the all-weather coat with or without the liner. They will wear the coat buttoned, except for the neck closure, which personnel may wear open or closed (unless otherwise prescribed by this pamphlet). Male and female coats are buttoned and belted from opposite directions. The black scarf is authorized for wear with the all-weather coat. Personnel may wear the coat with the service, dress, mess, hospital duty, and food service uniforms. The black, all-weather coat is authorized for wear with utility uniforms only in a garrison environment when personnel have not been issued organizational rain gear. Officers wear nonsubdued pin-on grade insignia on the shoulder loops of this coat. Noncommissioned officers wear shoulder marks on the shoulder loops. Enlisted personnel wear nonsubdued grade insignia on the collars. When the grade insignia is removed from the coat, personnel may wear the coat with civilian clothing.
The basic design of the Army all-weather coat has not changed since at least World War 2, though the regulation color at that time was khaki, not black. It was worn in the field
during World War 2, which is no longer the case. The modern place of the Army all-weather coat is with the sterile wear of fastidious Class A and Class B uniforms rather than the rough wear of rugged Class C uniforms. While its basic design has not changed since World War 2, I guess the contemporary construction of the Army all-weather coat is no longer rugged enough for wear in the field.
Due to the suggestive name and military origin of the coat, a common assumption is the gun flap below the right shoulder is related to firearm use, perhaps a vestige of a pocket for a pad to cushion the butt of a rifle. Actually, the gun flap covers the open edge of the convertible collar when buttoned at the neck to keep water from running inside the coat. It may be called a gun flap because raising the right arm, such as when using a rifle, tends to open a gap between collar and coat that lets in water. The gun flap is also called a storm flap, which better indicates its purpose. Closing the convertible collar does a good job holding body heat in the cold as well as keeping water out in wet weather.
The common name for the Army all-weather coat is the trench coat, derived from its use in the trenches of World War 1. More on the history of the trench coat here