Doc's writer, Lester Dent, was from La Plata, MO and said that the books were aimed at 15 year old boys. Forty years after that, I still enjoy them. Lester had to publish under a pseudonym, Kenneth Robeson. That pseudonym was also used for a series called The Avenger, which was not nearly as good, but also got republished in paperback in the 70s and 80s.