This pattern of denim jacket was adopted in 1917, but specification called for brown denim. This changed to blue denim in 1919. Some scholars think blue denim production started during WWI, prior to the change in specification, because of fabric and dye shortages, but research is still continuing. Although superseded by the 1940 denim uniform, this pattern was still widely worn and issued during much of WWII. This pattern was also widely used by the Civilian Conservation Corps, and many of these uniforms were worn as a combat uniform in the Philippines in the early days of WWII.