I think many of these types of things used to be secret in the past.

Such as Area51 was not a house hold name back when it started..
They use to say it was secret because they had to make large efforts
to hide their activity from Russian satellites.

They would mount jets on poles then measure the radar signature etc.
Then they knew when the Russian satellite was coming to look at them
then they would quickly hide the airplanes in hangars..
In an effort to hide the shape mostly i think.
But it did not work.. the full size airplanes in the desert sun would cast a shadow.
So when they removed the airplane the shadow was still a different temperature
than the rest of the surrounding area.. giving the Russians the exact shape that was a secret.