Literacy at what level? From your first source: "In 1940, more than half of the U.S. population had completed no more than an eighth grade education." The manu

Literacy at what level? From your first source: "In 1940, more than half of the U.S. population had completed no more than an eighth grade education." The manual had to be written at 8th grade level (at most) in order to be easily understood by more than 50% of the army.