Are We Giving Away Our State Secrets?; the Saturday Evening Post
Ciphers-by Herbert O. Yardley; the Saturday Evening Post
Codes-Article In the Saturday Evening Post
Cryptograms and Their Solution-by Herbert O. Yardley; the Saturday Evening Post
Double-Crossing America; Herbert Yardley Article In Liberty Magazine
Handwritten Note-Howell McConnell Mentioned
Handwritten Notes from Newspaper Articles
Secret Inks; the Saturday Evening Post