There was Zuma, the classified satellite that officially failed to separate from the payload adapter and burned up in the atmosphere but was widely speculated to be a successful test of stealth satellite technology, with the satellite successfully reaching orbit and going dark. A lot of talk about us knowing very little, but everyone loved to show off this graphic from a stealth satellite patent [1]. Of course if the NRO does a good job and the technology works we will never know that it does.
