TheCodeBreakers
It demanded the reconstruction of Code 0075, a two-
part code of 10,000 words and phrases numbered from 0000 to 9999 in
mixed order. Since a code is, in a sense, a gigantic monoalphabetic
substitution, the establishment of plaintext equivalents is the "only" task
involved. But where the cryptanalyst of cipher deals with only 26 such
elements, the cryptanalyst of code must keep his eye on hundreds or
thousands, whose characteristics, moreover, because of their reduced
frequency, are much scantier and more diffuse than the sharply defined
traits of letters.
Solution usually begins with the identification of the groups meaning
stop. Groups that recur near the end of telegrams are likely candidates.
The identification of stop or period is often aided because often only a few
of the many code equivalents are employed. Code clerks, referring
frequently to stop, come to memorize one or two of its codegroups; they
then simply use these groups in encoding instead of hunting up a
annaabi.ee 
