M-41 is the first notable field jacket adopted by the U.S. Army. It is referred to as M-41 because the pattern was established in 1941. Made of cotton poplin with a wool flannel lining, the M-41 is relatively lightweight, has a short length, and is designed for ease of movement. It was developed as a combat uniform for field use, offering a relatively casual style compared to other military uniforms. The M-41 features a double closure system with a front zipper and buttons. This design not only prevents outside elements from entering but also protects the zipper when the wearer lies on the ground. Early versions of the jacket had flap pockets on the front and lacked shoulder epaulets. However, the later Spec.20B variant, which gained popularity, eliminated the pocket flaps and added epaulets. The back of the jacket incorporates a pleat known as a "bi-swing," providing excellent maneuverability and functional detailing. This distinctive detail has been carried forward in successor models such as the M-43, M-51, and M-65 field jackets. The history of field jackets cannot be discussed without acknowledging the presence of the M-41 and its functional design elements.