This 
article from the Telegraph from 2014 dropped into my timeline today. It outlines the spectacular (and occasionally gory) knitting practices out there. There were women using knitting for code in the war, knitting at the guillotine, even an extraordinary set of islands in Peru that are basically knitted out of reeds. You can find the article at http://www.telegraph.co.uk/men/the-filter/qi/10638792/QI-how-knitting-was-used-as-code-in-WW2.html