I've seen a presentation (over 10 yrs ago) where passive radar was set up as a secondary sensor system that is hard to locate because it's not transmitting. On

I've seen a presentation (over 10 yrs ago) where passive radar was set up as a secondary sensor system that is hard to locate because it's not transmitting. One attack scenario is with a stealth plane first attacking the radar systems, then regular planes come in after. So the passive systems would stay up, as most attacks won't target civilian infrastructure. Still, there's a hint of hiding behind civilians here I don't particularly like. But I'm just being impractical about the matter. You can't optimize your civilian transmitters to send out signals best for radio detection and ranging, so you lose accuracy. Better than nothing.