Well, you know that the military has a lot of secret stuff you know nothing about right? Let’s use Area 51 as an example.
Leaks like Snowden or Manning are a drop in the bucket compared to the total amount of secrets that were not leaked.
As far as examples of successfully kept secrets, I can’t give those, because I’m in on it.
All a conspiracy is, is a group of people keeping a secret.
As far as conspiracies not being successful long term, history tells us no such thing. Conspiracies with tons of people are successfully kept every single day, only to be discovered decades later when something is declassified for example.
You can never prove if a conspiracy to keep a secret is not successful if you never knew it existed.
Am I making any sense?