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A2/AD Answers?

Two of the most important recent naval developments both relate to aircraft carriers: the flight of the U.S. Navy’s X-47B unmanned carrier attack aircraft in February 2011 and the advent of the Chinese DF-21D anti-ship ballistic missile.

At present only a carrier can deliver large quantities of conventional weapons from the sea on a sustained basis. A surface ship can launch a large salvo of cruise missiles – a Burke-class destroyer has 100 vertical launch cells – but the cells cannot easily be refilled at sea, and then only laboriously, in very calm water. By way of contrast, it is relatively easy to transfer weapons to a carrier, either horizontally (generally via an elevator opening) or via a helicopter, again with the weapon more or less horizontal. There is no need to thread it into a narrow launch cell. About two decades ago, U.S. Vice Adm. Joseph Metcalf, pressing for what he called a “Revolution at Sea,” pointed out that warships exist to put “ordnance on target.” He had cruisers loaded with vertical cells in mind, but carriers executing strike operations can be described the same way. A large U.S. carrier can accommodate about 2,000 tons of ordnance, and she can keep adding more from the fast replenishment ships that also keep her aircraft flying by supplying their fuel. Such ships may carry as much as 12,000 more tons of ordnance. In effect, the carrier and the string of replenishment ships are stages in the shipment of weapons from the United States to a distant target. They can keep hitting as long as the carrier and her aircraft survive. The X-47B and the Chinese missile represent two alternative answers to the question of how long a carrier can keep hitting targets.

Northrop Grumman’s X-47B is about the size of an F/A-18 Super Hornet. It is inherently stealthy, with the now-familiar kind of curved and blended fuselage and wings. Fly-by-wire electronics has made it possible to dispense with a vertical tail, an important source of radar signature. Because required control forces grow quickly with speed, X-47B is decidedly subsonic. However, in combat its high degree of stealth should give it considerable sustained survivability in the face of enemy air defenses. The airplane has two bays, each of which can carry either a 2,000-pound class weapon or additional fuel for longer endurance. In effect, X-47B represents an important choice for the U.S. Navy. The service could have decided to build a carrier-capable equivalent of, say, the land-based Reaper now being used effectively in Afghanistan. Reaper and similar unmanned aircraft have been used extensively to attack point targets such as Taliban leaders and squads. However, these low-performance airplanes would be unlikely to survive for long in any sort of sophisticated combat environment; they may even fall to hand-held missiles. If Afghanistan is the shape of future wars, then a carrier-based Reaper equivalent would make sense. If not – if the United States has to fight opponents with real air defenses, such as Iran – then such aircraft are irrelevant, and money spent on them will be seen as having been wasted as soon as the Afghan war winds down. The X-47B would seem to represent an understanding that counter-insurgency is not going to be the sole concern in future.

Northrop Grumman's UCAS (X-47B) AV-1. An unmanned strike aircraft could project power from great distances, possibly beyond the range of ballistic missiles. If unmanned refueling can be perfected – and it has been demonstrated successfully – then a swarm of unmanned combat aerial vehicles could operate at some distance from their carrier. Northrop Grumman photo by Chad Slattery

The X-47B test program is designed to show that the airplane can operate from a carrier. Thus the program calls for four different demonstrations: that the airplane can take off from and land on a carrier; that it can be handled on deck; and that it can be refueled in flight. It seems unlikely that any of the four will prove impossible. Carrier aircraft already land nearly automatically in bad weather and at night, controlled by the carrier. Operation on deck requires that the aircraft somehow recognize the usual commands from handlers. That may involve a below-decks controller looking through a sensor on the airplane, but at the very worst a crude pop-up cockpit can surely be installed so that a handler can climb on board once the airplane has been arrested. Takeoff is unlikely to be a problem. Many unmanned aerial vehicles (UAVs), such as the U.S. Army’s Warrior, already take off and land automatically – incidentally showing better safety records than UAVs using remote human pilots. Automatic in-flight refueling of other unmanned aircraft has already been demonstrated, and it appears to be more reliable than pilot-controlled refueling.

The most interesting capability designed into the X-47B is its control system. The airplane flies a preset path, which a controller can modify by data link. However, the controller never actually flies the airplane, as some large UAVs are currently flown. The controller is thus freed to monitor and control multiple UAVs. Moreover, the X-47B is conceived to operate in swarms. The swarm as a whole is assigned targets, and the appropriate airplane within the swarm to hit them (or to do other assigned tasks) is chosen by data exchange within the swarm. Because there are no human pilots to become fatigued, and because the members of the swarm can refuel in the air, the endurance of the swarm is limited only by the mechanical and electronic reliability of the airplanes. The swarm acts as a kind of enduring remote air base, its members returning one by one to the carrier to replenish their weapons.

This is not an entirely new idea. The Tactical Tomahawk missile already orbits awaiting instructions as to what target to attack. No human being flies each Tomahawk; instead, the swarm is given targeting instructions, and a targeting computer (typically on board a ship) decides which missile to send. The difference, of course, is that each Tomahawk has limited endurance and cannot be retrieved to be used again. In effect, X-47B is an evolved and reusable missile – or is it an unmanned airplane?

Looking at X-47B as a missile changes the way the carrier is perceived. The carrier becomes, in effect, a huge missile ship with the ability to launch again and again. It can project power from great distances by setting up its swarm within easy attack range of potential targets. The carrier’s own course is no longer a reliable warning to an enemy of impending attack. That uncertainty in turn greatly stresses any enemy’s ability to mount a defense. The U.S. Navy has long exploited exactly that uncertainty because the sea allows it such flexibility. A swarm of X-47Bs (or their production successors) would be a further step in that direction.

Moreover, unlike airplanes, missiles are flown only when needed. Years of experience show that pre-launch tests suffice to ensure a high rate of success. It would seem to follow that a carrier would not fly X-47Bs except when they were needed to mount attacks, or for equivalent tasks (such as reconnaissance). Furthermore, because no human ever actually flies the airplane, even remotely, there would be no need whatever for proficiency flying, or for flight training. Purchases of X-47Bs would be limited to those needed to fill the carrier force expected to deploy at any one time. There would be no training pipeline. Fewer than half as many X-47Bs would be needed as manned aircraft. Since the unit price of manned aircraft is beginning to raise questions about their viability, this sort of saving would surely be very welcome.

Overall, carriers are now both the most useful means of projecting U.S. power and the most expensive warships. Tactical aircraft accounted for something like two-thirds of the procurement cost of the ship four decades ago, when nuclear carriers had to refuel at least two or three times during their lives. Now that one-shot reactors promise to eliminate the costly refueling in new carriers, aircraft probably account for an even greater proportion of overall cost. Flying naval aircraft constantly, which is needed to maintain pilot proficiency, accounts for much more than half of overall aircraft costs. As now conceived and now being tested, the X-47B would eliminate much of that cost. Carriers would become not merely a prime way of projecting power but also a much less expensive one.

That would be fortunate, because the world is changing in a way that favors more, rather than fewer, carriers. The number needed is set not by the number of foreign carriers, but rather by the number of crises the United States must confront more or less simultaneously. During the Cold War, it was fair to assume that the Soviets would avoid provoking the United States by mounting multiple simultaneous crises. The number of carriers was set mainly by what would be required in a major war (the affordable fleet was never adequate). When the Cold War ended, naval deployment was set by the classical requirement that the United States maintain forces in both oceans. When fleet deployments were reviewed after 9/11, it became clear that there was a new problem of sudden unexpected crises; the 9/11 attacks fit none of the expected ones. Likewise, the recent explosions throughout the Middle East were entirely unexpected. To what extent would an enemy such as Iran try to exploit our preoccupation during an extended series of Middle Eastern crises, for example? After 9/11, the Navy developed a series of non-carrier strike groups to make the most of the fleet it had, but it was clear that none of them could be as effective as a carrier strike group. Anything that made carriers dramatically less expensive to operate, without costing striking power, would surely be very helpful. Land-based airpower does not generally provide a viable alternative because we lack overseas bases, and also because foreign governments may well decide not to allow us to use the ones we have.

In 1996, when the Chinese government threatened Taiwan, U.S. carriers provided Taiwan’s government with vital support. The Chinese were not happy. Their navy was already designed on Soviet lines, which meant that it was oriented toward extended coast defense. For example, the Chinese People’s Liberation Army Navy (PLAN) operated medium bombers, copied from the Badger (which had long been the mainstay of Soviet naval aviation), carrying standoff missiles. They were buying the much superior Soviet Kh-31 (AS-17) rocket-ramjet and supersonic fighter-bombers to deliver it. They were also developing an ocean surveillance system, probably based mainly on intercepting radio emissions from U.S. carriers – much as the Soviets had done during the Cold War. They demonstrated this system by having a diesel submarine intercept the carrier Kitty Hawk (the submarine could never have run fast enough to trail the carrier, so almost certainly it was cued by the surveillance system).

If war had broken out over Taiwan, the attack airplanes with their missiles would have been opposed by carrier fighters and by large numbers of defensive missiles. They might or might not have succeeded. However, the Chinese objective is not to fight, but rather to convince the United States to cede the Western Pacific, including Taiwan, to them. To do that, they must convince us and the Taiwanese that resistance is pointless, that they have a weapon so surpassingly effective that no carrier can be expected to survive interfering with their invasion of the island. Their new DF-21D ballistic missile seems to be their attempt to fill this bill.

DF-21D has a maneuvering re-entry vehicle that uses an on-board sensor to correct its path so that it explodes over a carrier. It makes up for inevitable inaccuracies by covering an extended area with sub-munitions. Proponents of the missile claim that although the sub-munitions would not sink a carrier, they would sweep its flight deck clear and cause sufficient damage to make further flight operations impossible. Some Chinese writers imagine further hits sinking the carrier, but that seems most unlikely.

Fortunately, ballistic missile warfare up to now has been limited to attacks by short-range missiles carrying conventional warheads. Despite some successes during the 1991 war against Iraq, and many subsequent successful tests, many do not believe that anything as impressive as longer-range ballistic missiles can be countered. Thus the Chinese leadership seems to think that hinting that the DF-21D has now been issued to the Chinese strategic force and launching ocean surveillance satellites suffices to eliminate U.S. carriers from consideration. U.S. Pacific Command’s Adm. Robert F. Willard seemed to play into this belief by stating that DF-21D was now operational and that it made operations in the Western Pacific problematic (the director of national intelligence later pointed out that the missile had not yet been tested against a moving target, and that it had been fired only a few times).

The U.S. Navy certainly has some interesting potential solutions to the DF-21D problem. First, it can counter the surveillance system without which DF-21D is useless. During the 1980s, the Navy devoted considerable attention to countering the Soviet ocean surveillance system, which to all appearances was considerably more developed than the current Chinese one. Solutions included carefully controlling shipboard electronic emissions (surveillance almost always requires a cooperative target), maneuvering when in radar range of a satellite (to change apparent radar signature), and various forms of deception, including confusing, dispersed formations. There is every reason to think that these measures worked. They were largely abandoned at the end of the Cold War, but they can and will come back.

A single modified Standard Missile-3 (SM-3) launches from the U.S. Navy Aegis cruiser USS Lake Erie (CG 70), successfully shooting down a non-functioning National Reconnaissance Office satellite approximately 247 kilometers (133 nautical miles) over the Pacific Ocean as it traveled into space at more than 17,000 mph. The shootdown of the satellite suggests the Aegis and SM-3 combo has the capability to shoot down an incoming DF-21D re-entry vehicle. U.S. Navy photo

Second is the ability to actually shoot down the missile. The defender has the advantage that the missile has a predictable path, because it has to head for the carrier on which it is homing. Chinese writers have stated that DF-21D follows a deliberately deceptive path, but that is unlikely, since it cannot maneuver very violently at its high speed without risking missing the target altogether. The missile has a limited payload, so to cover a large area it must make do with relatively small bomblets – or it has to home more precisely, and cover a smaller area. The harder the target – and a carrier is by no means a soft target, given its armored flight deck – the greater the need to use a smaller number of heavier bomblets, and thus to give up an evasive path toward the carrier target.

The U.S. Navy currently deploys the SM-3 anti-missile missile on board modified Aegis ships. SM-3 has performed brilliantly in tests and also in the single real-world situation it encountered: It destroyed a U.S. satellite tumbling to Earth, i.e., following an unpredictable path. The satellite was a lot larger than a DF-21D re-entry vehicle, but surely the unpredictability was a bigger problem than size. SM-3 has, after all, destroyed targets the size of that re-entry vehicle.

Third is standoff. The greater the distance from which a carrier can strike, the more sea room she has, and the more difficult the task of detecting and tracking her well enough to aim the missile. If the carrier were alone on the world ocean, detection would not be all that difficult, although connecting up detections by satellites on different orbits would still present problems. However, the larger the sea room the carrier enjoys, the greater the number of other ships that may be present. It may not be at all obvious to those operating the surveillance system which ship is which. That was certainly the case during the Cold War, and the physics involved has not changed.

After the Cold War, the U.S. Navy decided that long standoff ranges were no longer essential; deep attacks could be left to Tomahawk missiles and to the U.S. Air Force. That was why retirement of the A-6 Intruder and of dedicated carrier tankers was considered acceptable. As time passed, this decision began to be reversed, for example with the development of the Super Hornet. If the new X-47B can indeed be operated as a remote swarm and refueled periodically, then the standoff ranges achieved late in the Cold War (with thousand-mile strike flights by A-6s) will be handsomely exceeded.

Moreover, a stealthy attack UAV offers yet another interesting possibility. The swarm can orbit near wherever DF-21Ds are based: The whole point of stealth is that aircraft can live freely in the face of enemy air defenses. Instead of bombs, the airplanes can carry missiles intended to intercept DF-21Ds as they rise through the atmosphere, when they are most vulnerable. Boost-phase interception has long been the most efficient form of missile defense, albeit the most difficult to set up. It attacks a ballistic missile in the slow part of its trajectory. X-47B carries an efficient radar with an air-to-air mode. To counter this threat, the Chinese would have to disperse their missiles, yet coordinate their operation. That might not be easy.

The Chinese themselves may not be entirely sure that missiles like DF-21D spell the end of aircraft carriers, because they are investing heavily in building their own. They bought the Soviet carrier Varyag from its Ukrainian builder, supposedly to turn it into a casino in Macau. That story made it easier to obtain permission to move the carrier through the Turkish Straits, and it cut the ship’s cost to her scrap value. The parts of the weapon system planned for the ship had never been installed, and satellites showed that whatever had been placed on board was being removed by the builders. To all appearances, when she arrived in China the ex-Varyag lay unloved in a yard at Tientsin, the company interested in the casino having vanished. Then observable activity suddenly picked up. The ship’s island was transformed in order to be fitted with Chinese radars. This year smoke was seen coming from her funnel. Not only is the ship being fitted out as a real carrier, she is being armed as one. Recent Chinese statements confirm the reports that the country will be building more carriers from the keel up. It is difficult to imagine that a Chinese government convinced that ballistic missiles have finished carriers is investing heavily in building its own. Does it imagine that anti-carrier missiles involve some kind of magic whose incantations can be pronounced only in Beijing?

This article first appeared in Defense: Spring 2011 Edition.


Norman Friedman is an internationally known strategist and naval historian. He is the author of...