It is a size M.  Please check the measurements for size it may be closer to a modern S.

There is red staining on front of shirt, discoloration in underarms, some wear/split seam in one underarm.

The fabric feels like a 50/50 polycotton blend.

Please see all photos for condition.

Shoulders 14"

Sleeve 8"

Chest 38"

Length 20"

B120