I've read about a system they came up with when they were working on stealth, I think they may have it active, but I have no evidence.

The way Radar works is that it transmits a pulse of energy and then looks to see that energy reflected back.

Someone thought of putting small antennas on the skin of an aircraft, when a energy pulse hit the skin the antenna reported the frequency and strength of the energy pulse and the computer then generated a 'null pulse' at the same frequency, which canceled out the radar signal reflected back to the transmitting site, effectively making the aircraft invisible to radar.

Then someone suggested generating a null pulse at the visible light frequency range, light hits the skin of the aircraft, but it's not reflected back to the human eye.

I understand it's not perfect, you look and don't see the aircraft, but if you concentrate you can see a distortion.