Air Force chief of staff Gen. Norton Schwartz told the House Armed Services Committee in 2012, even the B-2 is starting to lose its ability penetrate hostile airspace. “The technology on which they were designed with respect to signature management . . . is ‘80s vintage,” Schwartz told the committee, adding, “the reality is that the B-2 over time is going to become less survivable in contested airspace.”
The B-21 design—which is similar to the original high-attitude optimized B-2 design—is built to counter the low frequency radars that can detect and track tactical fighter-sized stealth aircraft. Unlike an F-22 or F-35, which are designed to operate in an environment where the enemy might be aware of their presence, the B-2 and B-21 are designed to avoid detection altogether. Basically, the B-21 (and B-2 to an extent)—with its large flying-wing design—reduces its low frequency radar cross-section to the point where it blends in with the background noise inherent to those UHF/VHF band systems. That’s similar in concept to how a submarine hides in the background noise of the ocean. But—like all stealth aircraft—it will not be invisible. Stealth is not a cloak of invisibility, after all. Stealth technology simply delays detection and tracking.
The first B-21 planes will be powered by twin unaugmented F135 engines. Later versions will get new engines developed in the 2020s. This would likely mean the new bomber will be larger than a Boeing F-15E Strike Eagle or General Dynamics F-111 but smaller than the B-1 or B-2.
The B-21 has to have allowances for two feet or more of radar absorbent material coatings on every surface or the designers are forced to make trades as to which frequency bands they optimize the aircraft to operate in. As such, to defeat low frequency radars operating in the L, UHF and potentially the VHF bands (this is easier said than done—and could in fact be impossible), a flying wing design is in effect, mandatory.
The Air Force is planning on building significant electronic attack capability into the B-21 airframe (and the LRS family). Electronic attack capability is necessary to counter low frequency radars operating in the VHF band, which are nearly impossible to defeat with airframe shape and low observable materials alone. The fact is that despite the Air Force’s public narrative that aircraft like the F-35 can go into a high threat zone alone and unafraid, the service’s own experts at the Air Force Warfare Center recognize the value of jamming.