Lt. General David Barno and Nora Bensahel, scholar-in-residence at the School of International Service write about 10 dangerous "embedded assumptions" [1] in US military planning that could prove disastrous if mistaken. All are food for thought, but I found the fourth ("Stealth aircraft will remain stealthy") to be the most interesting from a strategic point of view. Right now, all branches of the US military assume that the US Air Force and the US Navy will be able to establish air supremacy prior to other combat operations. Stealth is a cornerstone of this capability. Without stealth, you lose the ability to degrade enemy air defense systems, and without the ability to degrade enemy air defense systems, you lose the ability to establish air supremacy.

Historically, our ability to establish air supremacy relied on two factors: stealth aircraft degrading enemy command and control systems, combined with SEAD (suppression of enemy air defense) missions to destroy enemy radars and open up holes in the enemy's defenses for strike aircraft to attack ground targets. The US military demonstrated this tactic to near perfection in the Gulf War, with stealth aircraft striking at command bunkers in Baghdad while specialized electronics warfare aircraft simultaneously opened holes in enemy air defenses by targeting surface-to-air missile radars. This was in stark contrast to Vietnam, where, thanks to underdeveloped tactics and technology, the US military was never able to fully establish air supremacy over North Vietnam, even though the North Vietnamese had relatively outdated export-grade Soviet surface-to-air missiles.

This is why technologies such as passive radar [2] (linked from the above article) are so interesting and worrying. Historically, due to signal processing constraints, radar transmitters and receivers have had to be coupled. This is significant because while receivers have expensive and valuable signal processing equipment (and often have even more expensive and valuable people monitoring said equipment), radar transmitters are basically overclocked microwave ovens. However, improvements in computing and signal processing technologies are allowing for the decoupling of transmitters and receivers, with a relatively small number of sophisticated receivers being able to integrate returns from a large number of "dumb" transmitters in order to create the same "picture" that one would gain from a single tightly coupled transmitter/receiver pair. In addition, many of these passive radar systems can use "transmitters of opportunity", allowing an air defense system to use civilian radio sources, like radio and television broadcasts or cell-phone towers as impromptu radar transmitters.

Why is this significant for stealth? As tacticians have pointed since the dawn of stealth aircraft, stealth is not invisibility. Stealth is camouflage. Low observability designs and radar-absorbent materials reduce the range at which observation is probable, but do not eliminate the possibility of observation. A good counter to attacks by camouflaged adversaries is to set up floodlights and motion detectors. Passive radar allows air-defense systems to do exactly that. The relative cheapness of transmitters means that an adversary can simply "tighten the net", eliminating the shadows and gaps that stealth aircraft rely on to sneak past defenses. Simultaneously the proliferation of transmitters and their physical decoupling from receivers means that SEAD missions will no longer be as effective as they used to be at knocking holes in enemy defenses. Finally, dual-use nature of these transmitters means that they can be located in civilian areas, further increasing the risks of SEAD missions targeting these transmitters.

The US military has long been operating under a modified version of Stanley Baldwin's famous dictum: "the stealth bomber will always get through". Technologies such as passive radar, combined with other innovations in visual and infrared tracking are increasingly rendering the modified dictum as false as the original. However, instead of recognizing this, the US military is doubling down on stealth, with the new B-21 and F-35 programs focused on building even stealthier bombers and strike aircraft. US tactics continue to emphasize the need to establish air supremacy, even as that requirement becomes more and more infeasible to achieve in practice. I fear that this will lead to a nasty surprise the next time the US has to fight a conventional war.

[1]: https://warontherocks.com/2018/04/the-u-s-militarys-dangerous-embedded-assumptions/ [2]: http://www.dtic.mil/dtic/tr/fulltext/u2/a515506.pdf