The use of these codes required the distribution of codebooks to military personnel, which proved to be a security liability since these books could be stolen by enemy forces.
[3] By the middle of World War I the conflict had settled down into a static battle of attrition, with the two sides sitting in huge lines of fixed earthwork fortifications.
The Germans started using trench codes in the spring of 1917, evolving into a book of 4,000 codewords that were changed twice a month, with different codebooks used on different sectors of the front.
He was one of the first to try to bring US Army cryptology into the 20th century, publishing an influential short work on the subject in 1915 called the Manual for the solution of military ciphers.
Another Signal Corps officer who would make his mark on cryptology was Joseph Mauborgne, who in 1914, as a first lieutenant, had been the first to publish a solution to the Playfair cipher.
When the Americans began moving up to the front in numbers in early 1918, they adopted trench codes[1]: p. 222 and became very competent at their construction, with a Captain Howard R. Barnes eventually learning to produce them at a rate that surprised British colleagues.
They learned to print the codebooks on paper that burned easily and degraded quickly after a few weeks, when the codes would presumably be obsolete, while using a typeface that was easy to read under trench conditions.