Plane Spotting During WWII

I came across a great booklet printed by NASA for the "Centennial of Flight" exhibits back in 2003. I got my copy at the Rockefeller Plaza exhibit. The booklet tells a concise history of flight from ancient times through the future. Of interest here is the discussion made on p.15 that civilian volunteers kept an "Eye on the Sky" and looked for any suspicious aircraft that could have secretly entered US airspace during WWII. This reinforces our belief that not only is spotting our right but could also serve a vital purpose. The ISBN # of the booklet is 0-16-067541-3 from the US Printing Office. I don't know if it's still available.