As several have pointed out, there are a number of ways ULF can defeat stealth: multiple detections over time and/or multiple ULF radars collecting returns from different angles of incidence. Or ULF can be combined with a different phenomenology: IR or UV, and let’s not discount very powerful UHF radars once within close-range of the target. So one operational concept would consist using multiple ULF radars plus advanced signal processing to produce something less than a track, say a target box or cone of probability. That information is handed off to a missile or aircraft which is vectored into the box whereupon high power UHF radar or IR guidance can become effective for the terminal phase of the interception.

But note the complexity of these chains, the demands they place on very high-quality C3, and the highly sophisticated and fast signal processing required. All these elements are required; the air defense chain will not work without each of them. I doubt whether Russia or China currently possess all of them or will in the near future. In any case, we will have plenty of warning since much testing of this chain will be required.

Plus all this coordinated sensing has to take place in an intense ECM environment, which no doubt will include offensive cyber attacks. Finally, the USAF and USN have always acknowledged that proper tactics are required to enable stealth technologies to function properly. Done well, strike aircraft will be routed to minimize the time and strength of exposure to sensors and control the aircraft’s aspects exposed to sensors. Finally, the aircraft and controllers hope to have collected the adversaries’ radars’ tell-tale waveforms, so onboard warning devices can notify air crews well before an air surveillance radar can return a detectable echo.

Finallly, note carefully the news fragments here and there on future USAF strike concepts. They envision the stealth aircraft being supported by lots of drones of different sorts. In other words, stealth aircraft are not expected to penetrate largely individually as they have been. They are now going to be part of strike packages of a sort.

Passive stealth technology has probably reached its limits with the F-22, F-35, and the next-generation bomber. Stealth is probably already well over the cost-effectiveness knee. But given all the “cards” they have to play, I don’t think the USAF and USN are being over-confident in anticipating another 10 to 20 years in the stealth era.

But I do hope they are planning intensively for what will come next, especially since 10 years could turn out to be five.