Authorized by the American Red Cross, this pattern was produced during World War I.
The description "morning blouse" indicates to me that this was considered at home wear.
The instructions on the back of the envelope explain how to make a flat felled seam, advising the maker to observe how the sleeves of a man's shirt are sewed into the armhole. This tells us that such seams were common in men's shirts but not in ladies' clothing.
I also thought the collar was interesting (and very nearly fashionable in its day)
Here is a front view of the blouse made up, both without and with the belt:
|From Unsung Sewing Patterns|