In February, U.S. and British aircraft struck Iraqi air defenses covering the "no-fly" zone. In recent months, the Iraqis had fired many more missiles at allied aircraft enforcing the zone. Moreover, Chinese engineers were installing fiber-optic cables linking different sites. It seemed likely that once this work had been completed, allied attacks would become far more difficult, as the air-defense system's integration, destroyed during the Gulf War, would be restored. Weapons used in the February strike included the Joint Standoff Weapon (JSOW, AGM-154) glide missile, as well as laser-guided bombs and AGM-130 electro-optically guided missiles. Reportedly, more than half of the JSOWs missed their aim points. The raid illustrated a new approach to defense suppression, and the possible failure of JSOW suggests problems with an important class of guided weapons.
First, the targets. In an unintegrated air defense system, radars at a given site must radiate to engage an airplane. Thus, the threat of an antiradar missile, such as a HARM (AGM-88, high-speed antiradiation missile), may suffice to shut down the radar and suppress the site. If the radar continues to operate, the HARM homes on it and damages it. The site is impotent until the radar can be repaired. If the radar shuts down to avoid attack, then the site also is impotent. The Israelis pioneered an approach to defense suppression in which an antiradar weapon loiters near the radar, ready to attack if the radar is turned on.
Integration negates such tactics, because a missile at one site may be controlled by a radar at another. Suppressing a particular radar may not open a safe corridor to attacking aircraft. Alternatively, several radars may turn on and off in a more or less random sequence, none of them staying on the air long enough to attract a missile. Netted together, the radars produce a good enough picture of air activity for missiles to be fired. Such techniques are particularly well adapted to command-guided weapons, which do not have to home on a target. The Serbians used such tactics during the Kosovo war, and reportedly they have advised the Iraqis on current air defense upgrade.
Even if an air-defense radar operates briefly, its position can be fixed either by interception of its brief signals or perhaps by analysis of imagery. If a missile can be fired to hit that fixed position, then the radar can be destroyed whether or not it happens to be operating when the missile arrives. Thus, it can be argued that the key to successful destruction of future netted systems is a class of missiles that can be targeted easily at known geographical positions, rather than at radar signatures (as in the case of HARM). Such a class is being created in the form of Global Positioning System (GPS)-guided weapons, such as JSOW and the Joint Direct Attack Munition (JDAM) guided bomb. Indeed, the United States seems to rely increasingly on GPS to guide weapons to particular geographical points.
JSOW exemplifies such weapons. It was conceived after the Bekaa Valley attack in the early 1980s, when Navy A-6 Intruders suffered losses because they had to approach their targets to hit them accurately. Worse, they had to do so at midday, when the defenders easily could see the approaching bombers. Although it was argued at the time that delays in the attack had caused the losses (a dawn attack probably would have been more successful), it was realistic to accept that political and operational factors often would make for poor timing. Attack bombers needed a standoff weapon they could deliver from outside defensive missile range. For simplicity, JSOW has no power plant (although there is provision for one, as a later upgrade) and no seeker. It relies entirely on GPS (satellite) navigation to bring it over an aim point. Once there, it spews bomblets over a substantial area. They should be capable of destroying not only a radar itself but also supporting soft-skinned vehicles and huts, so that the radar is suppressed permanently.
The only inexpensive alternative to GPS guidance is laser homing. It is quite easy to have a bomb or missile home on reflected laser radiation. Something, however, must illuminate the target. Not only must the illuminator come fairly close, but whoever wields the laser must be able to acquire the target in the first place, generally visually. From the point of view of the Bekaa attack, that would mean exposing the attack aircraft to relatively long-range antiaircraft weapons. From the point of view of radar defense suppression, laser guidance hardly would work. It would take considerable effort to find the appropriate visual aim points, given electronic detection of an intermittently radiating radar.
Of course, GPS is not the only way to bring a missile to a set place. For years, ballistic missiles have measured their positions using gyros and accelerometers, achieving impressive accuracy—a few hundred feet at a range of thousands of miles. The Navy's Trident missile uses star sightings to help establish its precise position as it emerges from the atmosphere, and thus to correct for any errors in measuring the launch position of its submarine. All inertial systems drift slowly over time, so they generally are considered unreliable for cruise missiles. Thus, Tomahawk was designed to navigate by comparing actual terrain altitudes with stored data. Although quite accurate, this system is useless unless elaborate digital maps of an area are available-which is often not the case. Inertial systems tend to be very expensive. They generally guide a missile to a set point at a set range and heading from the launch point, rather than to a geographical point. Accuracy demands precise knowledge of that launch point, which may not be available. Aircraft inertial systems, for example, are not nearly precise enough to determine launch coordinates well enough to bring a missile within a few feet of the known location of a radar.
GPS thus becomes very important in a world in which most radars are located by sensors other than the ones on board the aircraft attacking them. So the great question must be whether whatever disappointment was felt after the Iraqi raid can be attributed to some problem with GPS.
It is worth pointing out that according to some accounts the JSOWs that missed did so by perhaps a hundred feet, in which case the bomblets they dropped surely covered the targeted radar sites. There was some suggestion that the attack had been affected by a strong surface wind. It is most unlikely that the actual bursts of JSOWs were observed or, if observed, were precisely located. Deductions of misses presumably were based on observed patterns of bomblet dispersal. The higher the altitude at which a JSOW bursts, presumably the more widely its bomblets spread and the more they are affected by surface wind. As for the other weapons, they carry unitary warheads. It is easy to tell whether they hit their assigned aim points.
Assume that some JSOWs missed so badly that no mistake about their accuracy could be made. This was not the first time JSOW had been used, and in the past it has been quite successful. A miss might be due either to a GPS problem or to a mission-planning problem (the missile's destination is inserted into its guidance system by the airplane launching it, on the basis of software, which in turn goes into the airplane's mission computer). Some reports suggested that all of the failed missions had been planned by a particular unit, the implication being either a systematic human error or a bug. Or, perhaps, the planners compensated erroneously for known or imagined winds.
A planning software bug would be worrisome, because the planning system is tested prior to combat use. If it went undetected, that would bring the testing process into question. Since much of the software used to plan aircraft missions is closely related to software used to target missiles such as Tomahawk, any serious error would have fleet-wide implications. To make matters far more interesting, if indeed the missiles missed badly it may be difficult to say with any certainty whether the problem was in the planning software or in GPS itself. That the other weapons hit their aim points would prove nothing, since their human aimers would find it so easy to compensate for software errors that they might go entirely unnoticed. Past recent combat success with JSOW, however, suggests that the planning software works as intended.
That leaves GPS, which is the most worrying possibility of all. GPS is so widely used in U.S. weapons that its loss would be devastating. To a remarkable extent, it is the basis for the emerging network-centric approach to combat, in which sensors distinct from the attacking platform determine the location of a target, which can be engaged by a weapon designed to fly to a specified place on the earth. Incidentally, similar considerations apply to forms of mine countermeasures in which one platform finds mines and another destroys them. Without some means of knowing exactly where it is at all times, a sensor cannot effectively specify the location of a target.
GPS determines position on the basis of signals from the four closest satellites of the system. Since all are quite distant, the signals are weak. Although the antennas on the missile point up rather than down, a suitable jammer on the ground probably will pass its signal into them via their sidelobes. The Russians have been advertising exactly such jammers for some time, and the problem has been taken sufficiently seriously that the HARM missile has been modified to destroy GPS jammers. There are also anti-jam GPS receivers, but they are expensive, and they may not have been fitted to at least some JSOWs. Many weapons, including JSOW, have integrated inertial/GPS guidance, in which the inertial system takes over if GPS is disabled by jamming or other problems. In that case, accuracy would degrade visibly. One report rejected the possibility that the JSOWs had suffered from GPS jamming on the ground that surely U.S. intelligence would have detected it in advance. Given the likely value of such jamming, it seems ludicrous to imagine that anyone doing it would reveal it in advance.
The Iraqi experience probably will accelerate U.S. efforts to overcome potential jamming. One option is the adoption of costlier anti-jam receivers, but that will raise the unit costs of the weapons whose GPS guidance made them attractively inexpensive. Another option is to strengthen the signals of later GPS satellites. That is being done, but it will be decades before all existing satellites are replaced. Another option, unfortunately, cannot be implemented. As conceived, GPS had a coded military-only signal, offering greater precision. Coding was valued not only for secrecy but also because it made a signal easier to detect in the presence of jamming noise. The Clinton administration decided that the military-only signal would be released to the public, on the ground that better navigation offered advantages far too great to ignore. Finally, there is, of course, the anti-jammer missile.