We've had a lot of controvery here recently about how air defense systems fit together and the relative value of their components. I thought it might be helpful if I summarized how these beasts actually work so we can have the various issues in context. By the way, the title to this post reflects in-house think-tank world slang for such descriptions!

The backbone of an air defense systems is a series of command centers. At the lowest levels, these are Local Operations Centers (LOC) which simply gather information from sensors assigned to them and pass that up the true and also receive instructions and issue orders to the defenses. LOCs are very often mobile and in some cases built into the radar itself.

Next up the tree is the Sector Operations Center (SOC). This takes the information from the LOCs, deconflicts it (this means assembing all the LOC pictures, resolving any contradictions between them and ensuring that multiple reports of the same contact are identified as such) and adds in additional material such as safe routes for own aircraft, secure operating zones, details of prohibited and special-threat areas etc to construct a tactical picture of what is actually happening in the sector in question. Note that a LOC doesn't really know what is going on, it is reliant on the SOC telling it what is happening and putting its data into context.

One step higher is the Regional Operations Center or ROC. The ROC takes the tactical picture assembled by the SOCs and adds yet more data, of own operations, specific requirements, logistical considerations etc. Usually it is at this level that information from other services is added to the pool so that a rounded picture can be obtained. The ROCs then issue instructions to the SOCs who convert them into operational orders for the LOCs

Finally, at the top of the hill is the National Operations Center or NOC. This takes all the information from the ROCs and assembles a nation-wide picture of how the battle is going. A wise NOC does nothing but watch, intervening only if there is a matter of overriding national importance in question.

This all sounds very clumsy but it isn't, provided its computerized and works. If it is't and doesn't then the defense has problems.

The eyes of the air defense system are mainly its radars. The nomenclature we'll use here is the modern one wherein radar frequency bands run from A to P increasing in frequency as we go up. As a rule of thumb, the lower the frequency, the longer the range but the less precise the contact. The higher frequencies give us much more precise contacts but have shorter ranges and are much more restricted in their search ability. As we go from A to P, antennas get progressively smaller (P-band radars fit in the nose of small missiles).

The primary radars used are the long-range air surveillance radars (sometimes these are called Volume Search Radars or VSRs). Up to the late 1980s, these almost invariably operated in the E and F bands since this offered the best compromise between range and precision. Since the early 1990s, the D-band solution is becoming more popular since modern processing has greatly improved precision while D-band gives better coverage in bad weather and is more difficult to jam. These days VSRs are mostly 3-D systems; the old days saw two radars used for this role, a 2-D VSR and a seperate height-finding radar.

The VSRs provide long-range coverage (typically 300 - 400 miles) but their use is tricky. because their range is so long, their coverage is actuially quite spotty; things like mountains get in the way creating terrain shadows, the radars can't look into valleys etc. This can be reduced by placing the radar high up - eg on a mountain. the ultimate expression of that, of course is to put teh VSR on an aircraft. Another problem is lobing. Although most artwork shows radar coverage as a symetrical mushroom, this is far from the truth. In fact, coverage is a series of layered lobes (rather like the cross section on a hamburger) and its quite possible for an attacking aircraft to detect the null areas between these lobes and fly through them.

Another problem is datarate, the number of strikes per second that the radar gains on a given targe. For VSRs, this rate is low, often as low as six paints per minute. This means the track can fall behind what the target is trying to do. Yet another is deployability. These radars are large and relatively immobile (even the "mobile" ones can take a couple of hours to strike down ready for moving). Moving these radars is not a good idea for a number of reasons, one being that it makes deconfliction almost impossible.

Also, because of the terrain problems, the number of suitable sites is limited. Even then, there will be areas that are completely masked out by inconvenient mountains. These voids in coverage are usually covered by so-called "gap filler" radars that are positioned as needed and add their input to that of the primary VSRs. The LOC gets all this data and tries to make common sense of it before handing it up the chain.

By the way really good air defense systems have another level of radars that have ranges of 3,000 - 5,000 miles. These backscatter radars are so imprecise that they are only able to warn the network that something is coming; nevertheless, that limited role is very valuable, particularly in missile defense.

Once the order has been given to engage a target tracked by the VSRs, that target has to be located with enough accuracy to allow it to be fired on. This is the role of the Target Aquisition Radar or TAR. This takes the imprecise track of the VSR and refines it with great precision. TARs usually operate in the G and H bands and have data rates of around 1 paint per second. The TARs report to the LOC but their data does not usually go up the chain - their role is to ensure that the target is being tracked and its the LOCs job to ensure the TAR is tracking the right target. Once all that is done we go to the final stage.

For this we drop to the last class of radar, the Fire Control System or FCS. This is a high-frequency (normally I or J bands but increasingly K band) radar that doesn't scan. Its pointed at the target by the TAR and once contact is made, follow that contact only. The FCS can feed the range, altitude course and velocity data to anti-aircraft guns or steer missiles to targets or coach fighters into the attack.

So now we come to weapons (note, right at the end of a prolonged system). Some will be batteries of very long range missiles. these strike at high-altitude targets, those just entering the defended zone, those coming in along unanticipated routes or just launched to shake up the attackers. They have a lot of roles other than shooting down aircraft; they break up carefully calculated formations, force the attackers to burn fuel with evasive manoeuvers, add to the general air of gloom and despondancy. Its quite possible that inexperienced pilots under this type of attack will fly into the ground trying to evade missiles that are actually of little threat to them. The long-range missiles will have big warheads that can damage aircraft even if it doesnt kill them. These big missiles can be equated to barrage fire froma rtillery - the kill rate isn't high but thats not the point (although against an unsophisticated or careless enemy these long-range missiles can be devastating.

Intermediate range missiles basically provide area coverage against intruders. These are the workhorses of the system; they are the ones that brings specific aircraft under fire and attempot to stop them penetrating the system. Remember (this is very important) the function of the system is NOT to shoot down aircraft, its to make the results they achieve not worth the effort made to achieve them. An aircraft forced to abort is as much a success as one shot down; each aircraft forced to divert its efforts to attacking the ADS is as much a victory as one left burning in a field. In this world, numbers are key. The more missiles there are, the more sustained the assault on the attacking aircraft and the greater the variety of threats those aircraft have to face. Large numbers of missiles also gives the air defense system the option of putting batteries in non-optimum locations as nasty surprises.

Short range missiles basically defend key points. They defend the air defense system itself plus provide last-ditch defenses around airfields, SAM site and the various levels of OC. To some extent it may appear their deployment represents a failure of the Air Defense System since it implies that aircraft have actually penetrated the main defenses but actually this is misleading. The presence of the short-range missiles means that aircraft penetrating the net have to reserve enough combat capability to hande the last line. This can be the last straw.

Where do guns fit into this? Often dismissed as obsolete, tehy have advantages all of their own. They and their ammunition are cheap. They are not dependent on radars to work - if all else fails they can spew bullets skywards and hope. They are simple to operate. Their tracers scare the living daylights out of inbound pilots and may distract that pilot from the less obvious threat of an inbound missile.

The important thing is to see how interlinked and how interdependent this system is. The long-range systems break up attacks to give short-range system easier targets, Short range systems protect long range ones. Ground-based defenses provide safe havens over which airborne command posts can fly; the airborne command posts provide coverage that can't be matched by ground-based systems.

A curious thing about these systems is that, when they are subject to systems analysis, it becomes obvious that dramatic improvements in capabilities of one system component are virtually meaningless unless matched throughout the system. On the other hand, small, incremental improvements replicated throughout the air defense system can have a dramatic effect on capability. This is particularly true of communications - so much communicating goes on that even a small increase in its efficinecy significantly upgrades the system as a whole.

So there we have an Air Defense System. The systems integrator dusts the consoles and hands the keys to the national command authority and its up and running. And waiting.

By attacking an AD system's centers of gravity (the NOC and ROC in Stuart's post), you can dramatically reduce the "threat circles" posed by the remaining LOC's and SAM systems. In the Gulf War, this was accomplished using AH-64 Apaches, led by USAF pathfinder MH-53 PAVE LOWs, to fly nap of the earth and destroy ROC's before the first strike wave was launched. Once the major centers are eliminated, the rest of the system can be brought down more or less systematically with significantly risk and with fewer dedicated SEAD assets. Of course, this entire process is entirely dependent on the level of intelligence obtained regarding the location and function of the adversary's AD centers, and the development of a detailed plan playing against the weaknesses of that AD network in the war's opening hours. Without accurate intelligence, and a comprehensive and well rehearsed battle plan, taking down an AD system will be an arduous, costly process (witness our current unpleasantness). This underscores the importance of intelligence gathering assets such as the RC-135, EP-3, the retired ES-3, EF-111, and many others. The development and maintenance of sufficient numbers of these ESM aircraft is vital to the US way of fighting a war, and their present limited numbers are insufficient for the jobs required of them.

I disagree with one point of Stuart's however. I do not feel that merely getting a pilot to jettison bombs is the equivalent of shooting down an aircraft, at least not in the case where the US is one of the parties involved in the fracas. The US would much prefer to have an unsuccessful sortie where the pilot returns than lose an aircraft and possibly a pilot (I really think this applies to virtually any nation, except perhaps in time of dire national crisis). The pilot and aircraft who are not shot down will live to fight another day. It may be a pyhrric victory, but it beats taking a SAM up the tailpipe.

The USAF would much prefer to have the plane and pilot back even if it means an aborted mission. However, this is a classic example of assymetric perception between two sides. To the ADS, the objective is to stop the aircraft getting through to damage a critical target. Whether the aircraft in question is shot down, forced to abort or has to spend its time on defending other planes from the ADS is of no great consequence. The important thing is that the aircraft in question isn't going to be attacking something valuable today.

Looked at another way, the attacker has still made an investment in fuel, warload, pilot flying time, airframe life, whatever in getting that plane out. It got no return on (inflicted no damage with) that investment, therefore the attacker lost.

The way we assess these things in my end of the business is to designated aircraft actually shot down or so badly damaged that they are beyond economical repair as being "real attrition". These are assets that are gone and will have to be replaced. Sorties that are lost for any other reason, whether by being aborted or diverted to non-critical tasks, are "virtual attrition". Now, the value relationship between real and virtual attrition is variable and depends on circumstances. As you point out, to the USAF, there is a world of difference, to the air defense system crews, there is almost none.

Virtual attrition can result from quite subtle interplays. For example, the Iraqi SCUD missile attacks on Israel and Saudi during the Second Gulf War caused literally hundreds of aircraft sorties to be spent in chasing around looking for missile TELs rather than pounding on the Republican Guard. Those strikes that didn't happen were all virtual attrition attributable to the missile attacks.

Virtual attrition doesn't even have to be caused by an airstrike being diverted or aborted. For example; take a section of four aircraft each with four hardpoints (two under each wing) trying to penetrate an air defense system equipped with missiles and deliver 16 bombs to target. To do so, it needs a jamming pod. That takes up one hardpoint per aircraft. The warload on each bird is now reduced from four to three, meaning we have to add an extra aircraft to maintain the weight of attack. That extra aircraft is virtual attrition - if it wasn't here it would be doing something else. If the ADS now has fighters (even MiG-21s), those bombers may now have to carry an AIM-9 for self defense, cumulatively reducing their hardpoints from four to two. We now have to use eight aircraft where four were previously necessary. Looked at another way we can only hit half as many targets as previously.

The USAF is fortunate in that it has so many assets that it can accept a high level of virtual attrition without flinching. Other air forces are not so lucky. If they have only limited assets to begin with, virtual attrition can neutralize the air force almost without firing a shot. The ADS wins simply by being there. By the time the assets needed to protect the bombers are allocated, there aren't any bombers left to protect.

It also explains why we employ 600 sorties per day in Kosovo but only about 250 actually drop anything. And most of those only drop one or two. Everything is either fuel or defense supression for the most part.

Add in that the SAMS tend to force the planes down in altitude to where the guns are the most effective. The single system most feared by US aircrews is the ZSU-23, when coupled with an SA6 it is a very dangerous combination. That combination for a time defeated the Israeli AF and almost turned the '73 war.

In NATO the hierarchy of posts goes from Control Reporting Post (CRP) to Control Reporting Center (CRC) to Sector Operations Center (SOC) to Regional Operations Center (ROC). The ROCs are the senior warfighting level and feed the SHAPE HQ the overall picture. There is also now the Combined Air Operations Centers replacing ROCs. The SOCs, ROCs and CAOCs do all air operational planning and will issue the Air Task Order as appropriate.

In NORAD the radars directly feed the Sector Air Operations Centers (SAOCs - Being renamed Sector Battle Control Centers) where all the tactical action occurs, then to the Region Air Operations Centers (RAOC) which conducts overall air operational planning and execution, which then feed the Cheyenne Mountain Operation Center (CMOC).