From the Decades of Style website:
Just wait until you see this vintage pattern made up! You will want to wear your muslin - it is that good. One collar was not enough; this blouse has 3 collars stacked upon each other.
It is a simple sheath with a cap sleeve and invisible side zipper. Darts and tucks provide shaping at the waist. Decorative running stitches of embroidery floss on the collars and armhole.
Suggested fabrics: Light weight fabrics only as there will be quite a few layers to sew through when attaching the collars. Linen, broadcloth, rayon crepe.
It is fine without them - but it is the 1940s- so you can add a little shoulder pad if you want.