Commercial Art, War Dept. Style
During World War II, the Armed Forces required many specialists and laborers. If you went to art school before entering the service, there was a good chance you might be placed in a graphics unit producing anything from posters to manuals to camo and more.
Commercial art was one of many jobs available to draftees and enlistees. The manuals used for training were similar to the correspondence school genre that civilians used to learn basic skills.
Not every soldier fought with a gun and bayonet. And design was a craft that could easily be used in peacetime, too.