The cap was originally used by the CCC as a working cap in the 1930s, made of blue denim, and was issued for a time at the beginning of WWII. It was replaced by the olive color cotton herringbone twill working cap in 1942.
It's made from 9 oz selvedge denim, with cotton herringbone twill fabric tape reinforcing from the inside. It has a high reduction degree for the original version.
