I had the honor of working with, years later, the group who developed the navigation system for the SR-71. The SR-71 was such a secret, and kept so, that when it first flew over the Soviet Union, they panicked. They sortied their Norther fleet and mobilized the army. It was like stirring an ant hill. Years later, the US learned from a defector that the Soviets saw this thing, obviously under control, flying almost in orbit and faster than any known craft by far. They thought it was an alien space ship. That’s how secret it was kept. And, by the time it flew probably hundreds or a thousand people had been briefed. Nobody talked.
A Russian refugee told me, “There are no secrets in America. The moment the second man learns a secret he’s off looking for a book deal.”
My mother’s uncle worked in Palmdale for Northrop and he never told anyone what he did. He’s been dead for 30 years and still no one has any idea what he actually did there.
Some people knew how to keep secrets.
I used to sell video production gear to Lockheed, in Burbank. In the normal course of schmoozing the customer and showing my face, I occasionally entered secured areas. Whenever that happened, 11 CAD/CAM engineering guys in their cubicles stood up, their CRT screens all showing “uncleared visitors” in area. It probably cost them a few grand in blown off salary costs just showing me around the plant.