During World War I there were several instances where steganography was used with success. One method was called a Turning Grille, which enhanced Cardano's Grille. It looked like a normal grille, a square sheet of cardboard divided into cells with some of the cells punched out. To use the Turning Grille, the encoder would write the first sequence of letters, then rotate the grille 90 degrees and write the second sequence of letters, and so on, rotating the grille after each sequence.
The Germans provided their troops with different grilles to be used for messages of different lengths and code-named them based on the number of letters in each grille. The French were able to devise an attack against this system, and the grilles lasted only four months.
World War I was also a time in history when cryptography made a giant leap forward. Radio communication, which was used for the first time in a major war, was the biggest contributor to both the need for better cryptography as well as better cryptography security.
Another instance of steganography during World War I was when a woman suspected of working for the Germans was found with a blank piece of paper in the sole of her shoe. As it turned out, this "blank" piece of paper had a message written on it with invisible ink. The message was quickly revealed because it was written in a heat-based invisible ink. From that point on, the Germans quickly got much more clever and began hiding their messages in garments such as scarves and socks.
Invisible ink subsections were created within the War Department, and a back-and-forth battle began between the Allies and the Germans. At one point in time, 2000 letters a month were being tested, 50 of which had invisible ink messages that proved useful.
There was also a record of a cable censor who received the message "Father is dead." The censor changed the message to "Father is deceased." A reply came back, "Is Father dead or deceased?" Other forms of jargon code were also used during World War I. A British censor was responsible for discovering two German spies when he became suspicious of a large number of cigar orders. The cigar orders were the spies' covert communications, using the numbers and types of cigars to code ship movements. Because of the large volume of cigars that were supposedly being shipped, attention was drawn to their activities. The censor exposed the spies, who were later captured and executed.