Here is an anecdote that I recall reading as a child:
During World War II, the English found a way to smuggle microfilm past the German authorities. They sewed a hollow button to their jackets that could be unscrewed to reveal a tiny, secret compartment. Eventually, the Germans found out about this hiding spot, so the English came up with a new trick. They reversed the thread, so the Germans couldn't work out how to open the buttons.
Now, even as a child, I found this startling. Imagine risking your freedom based on whether a German guard slavishly followed "Lefty Loosy, Righty Tighty". As an adult, colour me skeptical.
So, my question is: Did this really happen?
A more modern example of the claim comes from a 2013 Car Talk episode:
RAY: There were a lot of things they could have done. They could have applied some adhesive making them difficult to turn or they could have put some kind of a locking pin. But what they thought of was even better. They made the threads.
TOM: Left hand thread.
RAY: Exactly. So when the Germans twisted the buttons, they in fact didn't come off, they got tighter. And after they failed in a few attempts, they gave up on it because they just figured out, they're not using that trick anymore.
Their version says "Allies", rather than English, and I am nervous about relying on my memory on this point.