These articles, previously classified, appeared in various issues of The Signal Corps Bulletin. Included in Vol. 1 are "Cryptanalysis" by William F. Friedman, "Problems of Code" by Marcel Givierge, "Solution of The Playfair Cipher" by Alf Monge, and "Analysis Versus The Probable Word" by Howell C. Brown. Two pages of Playfair Cipher problems for the student have been added to the text.