Hidden beneath the floors of a house from the 1930s
Given that the house is from the 1930s, it’s likely that this person served in Army after the Civil War. Although, we’re not confident if he had seen more on the actual battlefield or found this piece in the bathroom – where OP discovered it.
The “Swiss blouse,” designed by an assistant surgeon, was authorized for use on the field by the United States Army. This apparel was distinguished by four pleats that fell straight down each frontal side from the shoulder to the bottom of said skirt.