My - when I see the term “Open-source” I’m usually thinking of something like Linux software - not a nuclear think tank!
Wow!
I think of nuclear war 24/7
Source means "source of information". "open" means they aren't concealing their identity for fear of blowing their cover. Some information can't be divulged because the number of persons who have access to it are so limited that the origin of the compromise would be easily discerned. That's a quick way to lose a source...usually to a room temperature condition. Other information isn't divulged because you don't want the observed parties to be aware that you have a means of observing them.