Did you know that during World War II knitting was used for codes.  I saw a post in one of my groups and wanted to check it out more and found several articles.  I think this is amazing.

Here are some of the articles I found:

QI: How knitting was used as code in in WWII

Knitting in code  first article on the left

Historical Craftivism, Knitting and WWII

Those are just a few but they are interesting.