“The officers in charge of the code rooms would remind us constantly to keep our mouth shut. Don’t even mention one thing about where a message came from and certainly nothing it said. And they’d say, ‘Now when you have a top secret clearance that is what it means, top secret. Keep your mouth shut.’ So we got reminded a lot.”

The Sigaba machine made plain information a secret language to those who lacked the equipment to understand it. The one that Helen Niebouar operated was a complex device. The National Cryptologic Museum displays both early and modern tools that have been used in secret communications.

One display at the museum explains American attempts to read Japanese military information during World War Two. Japan’s Navy used special machines to change its written information into secret codes. This coded information was then sent by radio to navy ships and military bases. The information included secret military plans and orders.

The leaders of the Japanese Navy believed no one could read or understand the secret codes. They were wrong. Americans were working very hard to learn the Japanese code. The United States urgently needed to break the code to learn what Japan was planning.

In 1940, an American woman named Genevieve Grotjan found some information being repeated in Japanese coded messages. At the time, she was a civilian working for the government in Washington, DC. Her discovery helped the United States understand secret Japanese diplomatic messages.