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Will Stealth Survive As Sensors Improve? F-35, Jammers At Stake

Posted by Sydney J. Freedberg Jr. on

F-35B with asymmetric weapons load
[Corrected 9:35 pm with a note about the EC-130 Compass Call] Is stealth still America’s silver bullet? Or are potential adversaries’ radars getting too smart for US aircraft to keep hiding from them?

That’s literally the trillion-dollar question, because the US military is investing massively in new stealth aircraft. At stake in this debate are not just budgets but America’s continued ability to project power around the world.

With the B-2 bomber, the F-22 Raptor, the F-35 Joint Strike Fighter, and a future bomber system known as Long Range Strike, the Air Force has bet its future on an all-stealth combat fleet. After the Navy’s troubled A-12 stealth plane program was cancelled in 1991, by contrast, the sea service kept buying conventional aircraft, the F/A-18E/F Super Hornet.

Now the Navy is gingerly getting back in the game with its experimental X-47 UCAS attack drone and the carrier-borne version of the F-35 — but it still harbors doubts about stealth. Meanwhile the Air Force worries its non-stealthy Navy partners will get shot down on day one of the next big war. So while the two services are ostensibly joined at the hip in an emerging combat doctrine known as AirSea Battle, they have radically different approaches to a fundamental question of how their airplanes can survive.

“There are not just the issues of technology involved but there are political issues, acquisition process issues, as well as budget and institutional issues that are all in play,” said retired Lt. Gen. David Deptula, a member of Breaking Defense’s Board of Contributors and the first man to serve as the Air Force’s head of Intelligence, Reconnaissance and Surveillance. The Navy F/A-18 is “fine in the kind of threat environments that we’ve been used to operating in over the last 20 years,” he said, against relatively backward foes like the Taliban or even Saddam Hussein, “but [non-stealthy] fourth generation aircraft — F-15s, F-16s, F-18s — are not survivable in a modern double digit surface-to-air missile environment.”

Others are more cynical about stealth. Argued Norman Friedman, a noted analyst who’s worked for the Navy, “the Air Force went hot on stealth because it was a way of showing that pilots could survive” in the face of improving anti-aircraft defenses known as “dougle-digit SAMs,” the highly capable air defense systems that the Soviet Union began developing in the 1980s.

“A lot of this is about whether pilots stay in business,” Friedman went on. Especially outside the Air Force, he said, “I would suspect that people worry about stealth not being nearly as good as people claimed it was. The CNO in Proceedings said as much.”

No less a figure than the Chief of Naval Operations, Adm. Jonathan Greenert, a submariner, wrote in the nation’s most prestigious naval publication, the Proceedings of the US Naval Institute that “sensors will start to circumvent stealth” in the future.

“The rapid expansion of computing power also ushers in new sensors and methods that will make stealth and its advantages increasingly difficult to maintain,” Adm. Greenert wrote in July. “It is time to consider shifting our focus from platforms that rely solely on stealth.”

So while the Air Force has bet on stealth to hide its planes from hostile radar, the Navy is still buying electronic-warfare aircraft to neutralize radar the old-fashioned way, by jamming it. Those Navy jammers also support Air Force operations and are even crewed, on occasion, by Air Force personnel – but the Air Force has no jamming aircraft of its own.

[Note: After this article went online, several astute readers brought up the Air Force’s EC-130 “Compass Call” aircraft (see the comments section below). While the EC-130 was primarily designed to jam enemy communications, it does have some capability to jam enemy radar as well, at least in later versions — the Air Force is naturally cagey about its exact capabilities. But there are only 14 EC-130s in the entire Air Force; by contrast, the Air Force had 42 EF-111 Ravens before those were retired, while the Navy has 79 of a planned 114 EA-18G Growlers today and, together with the Marine Corps, retains about sixty of the older EA-6B Prowlers, though more are being retired every day. Compared to Ravens, Growlers, and Prowlers, the EC-130 also lacks the speed and agility to accompany strike fighters into hostile airspace. All told, “Compass Call” is impressive, but it’s a niche capability in this context.]

Performance specs for stealth versus radar remain a carefully kept secret, for obvious reasons. But Breaking Defense did speak to (among others) two of the leading experts on the subject: F-35 booster Deptula, a retired three-star general with decades of experience planning and flying combat missions; and long-time stealth skeptic Friedman, an award-winning military analyst and author with a degree in theoretical physics. The two men have very different takes on the future viability of stealth – but both agreed, to start with, that it’s not the magic invisibility cloak from Harry Potter.

“People need to understand stealth is not invisibility,” Deptula told Breaking Defense. As current sensor technology improves, he said, “you’re going to be able to detect aircraft with current levels of low-observability at further distances.” That said, non-stealth planes are much bigger targets, he said: “It’s a piece of cake for an adversary with a sophisticated air defense system to engage and kill a 4th generation aircraft; it’s very difficult for them to do that with a 5th gen aircraft. Will it get easier in the future? Possibly.”

“You can’t make something disappear, all right?” echoed Friedman. “What you can do is reduce the signature you get back [on the enemy’s sensor screens]. More powerful processors buy you back part of the signal” – and thanks to Moore’s Law, the processing power available to do that doubles every 18 months. The more powerful the processors and the more sophisticated their algorithms, the more effectively they can sift meaningful data out of the static. And no matter how stealthy an aircraft is, it still makes some noise, it still emits some heat as infra-red radiation, and – most critically – it still reflects back some portion of an incoming radar beam.

Not that all radars are created equal. Even back in the 1980s, author Andrew Cockburn warned that, ironically, the Soviet Union’s oldest, crudest radars might detect stealth bombers that newer systems missed. Stealth aircraft rely on carefully designed shapes and thin surface coatings to baffle incoming radar beams. But the lower the frequency of the incoming radar, the longer the wavelength, which means the less it reflects such subtleties at all: It’s essentially too stupid to be tricked.

The upside is such relatively crude radars may detect a stealth aircraft is out there somewhere, but not accurately enough to shoot it down. The low-frequency, long-wavelength radars that are most likely to see through stealth are, for the same reasons of physics, the least precise. They’re also too big to fit in anything but a ship or a fixed ground installation, where they are typically used to give warning that aircraft are in the general area. Actually tracking and hitting a target depends on smaller, shorter-wavelength radars which can fit in, say, an interceptor aircraft or surface-to-air missile and which offer more precision but are also more easily baffled by stealth technologies.

“Just because you can see someone now doesn’t mean you can kill them,” said Deptula. “Acquisition radars, which are what people generally tend to focus on, are only one element in an adversary’s air defense equation.” After a target is initially “acquired,” he went on, “you need to be able to track the asset to then get to a firing solution; then you need to transfer that tracking data to the missile, which then needs to be able to acquire and track the aircraft [after it launches]. Presuming that the missile can track… now the fuse needs to be able to detect the aircraft” in order to detonate at the right time.

Break any link in that “kill chain,” and the stealth aircraft survives, even if it’s seen. So while stealth can’t defeat all the radars all the time, it doesn’t need to.

The problem is what happens when all the radars are working together in parallel instead of in a series. Rapid advances in computing technology don’t just improve the individual radars. They also make it easier to share data among multiple sensors of multiple types – radar, infra-red, visual, acoustic – and thus put together scattered clues into a picture that’s clear enough to kill.

“If you have a lot of radars working together, then you add up all of those very momentary detections and you get a track,” said Friedman. With a command-detonated or time-fused missile instead of a radar-homing one, he went on, you can then fire at the predicted position of the target, without needing a radar lock on its precise location. This technique is less precise – the equivalent of shooting at a strange noise in the dark instead of having the target in your sights – but it can be effective. It may, for example, have been how the Serbians shot down an F-117 stealth fighter during the Kosovo air war in 1999.

The issue is not just technology but tactics. Stealth aircraft still need to aim for the weak points in an enemy air defense system to fly through the gaps in radar coverage; it’s just that those gaps will be larger for them than for conventional planes, because the enemy radars can only detect them at shorter ranges. Conversely, non-stealthy aircraft can still penetrate sophisticated air defenses — if there are enough of them to take losses and still complete the mission, and if they’re accompanied by enough jamming aircraft to blind and baffle the enemy radars. The question then becomes whether a small number of stealth planes gives you more bang for the buck – and fewer US casualties – than a larger force of non-stealth ones.

Sure, said Deptula, “it’s less expensive on a per-unit cost basis to buy more F/A-18E/Fs or new F-15s or new F-16s than to buy F-35s or F-22s — but when you get all of those fourth-generation aircraft shot down the first day, what’s your cost-effectiveness now?”

While a large enough armada of non-stealth strike planes and escorting jammers can batter their way through enemy air defenses, Deptula said, “you’d have to put together a significant force package with many aircraft to do the same job as a handful of fifth-generation jets [like] F-22s and F-35s.” In the future, as enemy sensors keep improving, the 5th gen stealth planes might eventually need some jammer support themselves, he acknowledged, “but they’re going to use a hell of a lot less.”

In fact, while jamming has been done usually by special-purpose aircraft like the Air Force EF-111 Raven (retired in 1998) or the Navy EA-6B Prowler and its replacement, the EA-18 Growler, fans of the F-22 and F-35 argue the new planes can scramble enemy radar on their own. Thanks to the same increases in processing power than make radars more sensitive, electronic warfare systems that once took up an entire airplane can now be miniaturized and fit aboard a fighter-bomber as just one weapon among many. For example, the F-35 possesses powerful jammers and highly classified electronic warfare capabilities, as well as boasting layers of designed-in low observability (aka stealth). Exact capabilities are highly classified, but proponents say the latest systems can not only tell where an radar beam is coming from but can also feed back subtly scrambled signals, misleading enemy sensor operators who may never even realize they’re being jammed.

“We have to get beyond the notion that 5th generation aircraft are single-role aircraft,” said Deptula. “They’re actually flying sensor nodes; they can collect ELINT [electronic intelligence], SIGINT [signals intelligence]; they can launch anti-radiation missiles” to home in on enemy radars and destroy them. “They can carry a panoply of different weapons,” he said. “They give us the potential to create a networked airborne ISR strike complex that has significantly more capability than operating concepts of the last century.” New technologies require new tactics.

Of course, this multi-functional flying network still requires the individual aircraft to transmit radio messages and, at least to some extent, to send out radar beams and other “electronic emissions” – all of which can be detected. A technology known as “low probability of intercept” is designed to make a stealth plane’s radar and radio emissions harder to detect by minimizing power, hopping frequencies and scrambling signals, but the enemy can improve his sensors in turn.

“The way LPI usually works is you send out a signal that looks like noise and somehow you reassemble that signal when it comes back,” said Friedman. That depends on massive processing power and sophisticated algorithms – which are becoming more available to everyone. Are you so much smarter in your processing than the other guy?”

But Friedman believes stealthy aircraft should not emit. “The more stealthy you want to be, the less you want to emit.” Therefore it’s better to have dedicated, non-stealthy electronic warfare aircraft as backup – presumably at a safe distance from enemy missile launchers – or, better yet, expendable decoy drones that emit enough to draw attention and draw fire away from the actual manned planes. (Of course, at this point, grumbles Friedman, why not make all the aircraft unmanned?)

So while stealth is no longer a silver bullet – if it ever was – it is still useful. It just needs to be used in conjunction with smart tactics and with other technologies. The challenge is not to let the increasingly expensive airplanes crowd all the essential supporting systems out of the budget.

It was budget pressures — and top brass’s desire to prioritize the F-22 and F-35 — that led the Air Force to retire its last electronic warfare aircraft, the EF-111, and later to abort an effort to convert B-52 bombers into jammers. Cost considerations even led the Air Force to skimp on buying secure datalinks essential to the “flying network” tactics Deptula advocates. Now, as money gets tighter and sequestration looms, budgeteers need to save their top priority programs and do it without slashing the small-but-essential items that make the big stuff work.

What do you think?