A single specification was issued for the new sports design that included both cotton and flannel shirts (Khaki Cotton Shirt and Coat Style Olive Drab Flannel Shirt, Specification PQD 96A dated 8 October 1941). Issuing a single specification for both shirts enabled manufacturers to produce either type without needing to change their plant equipment or assembly process. This practice helped the Army prepare for and meet increased production demands in times of emergency.
Though the basic design was set, the flannel shirt would see several changes throughout the war years. During March 1942, special gas protection features were added in the form of a flap behind the front closure, gusset-like pieces of material behind the cuff openings, and two buttons behind the collar for attaching a hood.