The A to Z Challenge asks bloggers to post 26 posts, one for each letter of the English alphabet, in April. Most of us choose to make these posts on a particular theme. My theme for 2022 is Codebreaking in World War II, which fits with the topic of the novel that I’m writing. Visit every day (except Sunday) in April for a new post on my topic.

T is for Traffic

All the glory in codebreaking goes to breaking the gobbledygook of symbols to read the hidden message. But it turns out that you can learn a lot simply by analyzing the traffic of messages that are sent over the radio waves. That’s called traffic analysis.

Here’s how “traffic analysis” is defined in Code Girls by Liza Mundy:

[Women] pushed forward new fields such as “traffic analysis,” which is a method of looking at the external features of a coded message—the stations where messages are being sent from, or to; sudden fluctuations in radio traffic; ominous silences; abrupt appearances of new stations—to learn about troop movements. (p. 19)

When I was a budding computer programmer in the early 1980s, I learned how World War II accelerated the development of computers. We weren’t quite there yet at the end of the war, but there were definitely machines that could be called proto-computers.

The Other Ultra (aka The American Magic, in the US) by Ronald Lewin explained how machines built by IBM were used in traffic analysis:

By the beginning of 1944 records were being kept on IBM machines of every individual radio contact between Japanese stations. Weekly and monthly tabulations showed the place of origin, the destination, the cryptographic system and the number of messages intercepted. Here was a potent ally for the code breakers in the task of fixing the location and following the movements of, so far as possible, every unit in the Japanese Army. (p. 198)

As I pointed out in my I is for IBM post, Lewin neglects to point out that those IBM machines were run by women.