Technology Explained – Desert Storm Electronic Battle Pt 3

The Texas Instruments AGM-88 is a development of a seventies program to improve on the Vietnam era Shrike ARM. The HARM became operational with the USN’s A-7E in 1984, and is a substantial 363kg (800lb) missile with a range well in excess of 19km (10nm) and aspeed in excess of Mach2. The important aspect of HARM is its intelligent (Texas Instruments) broadband seeker, which covers frequencies from the lower microwave band well into the upper Jband, and is quite capable of sorting, identifying and prioritising threats for attack autonomously. High directional accuracy is achieved with a nose mounted cavity backed conical spiral antenna, a class of antenna conferring coverage from C to J band. The autonomous seeker was sought primarily by the USN which could not afford the luxury of dedicated SEAD platforms, therefore every aircraft was seen as a potential launch platform.

Unlike conventional guided munitions, the HARM must communicate with the aircraft’s radar warning (or homing) equipment and the aircraft’s crew, therefore the missile is supported by a dedicated launch computer, the Command Launch Computer (CLC) in USN/USMC service and the Aircraft Launcher Interface Computer (ALIC) in USAF F-16 aircraft, tied typically to the aircraft’s Mil-Std-1553B digital databus. Via a bus the CLC/ALIC receives data from the missile and the aircraft’s EW systems, and in turn sends messages to the mission computer for display to the crew. A typical installation is that in the F/A-18, which employs a LAU-118/A launcher attached to a BRU-32/A bomb rack, the LAU-118 providing the required umbilical interface to the HARM.

Tied to the CLC the HARM has three basic modes of operation. In Self Protect Mode the missile is locked onto an emitter which it is cued to by the launch aircraft’s onboard receiver, in Target of Opportunity Mode the HARM autonomously searches for targets which are displayed to the pilot by the Command Launch Computer, and finally in Prebriefed Mode the weapon is fired against a planned target. The USAF F-16 ALIC supports three modes, Position-known (POS), Launch-Off-RWR (LOR) and HARM-as-Sensor (HAS), similar to corresponding USN/ USMC modes.

Only aircraft fitted with the CLC/ALIC and with appropriate software to interface the mission/fire control computers to the CLC/ALIC can fire the weapon, others cannot.

Once launched the HARM will home in on the selected emitter and detonate either on impact or near miss, earlier models fitted with a conventional blast fragmentation war- head, newer models (AGM-88C-1) with a prefragmented tung- sten case warhead designed to perforate radar vans with tumbling high velocity fragments, to disable personnel and electronic equipment rather than simply strip off antennas and aerials, allowing later repair. The HARM uses a Motorola DSU-19 active optical proximity fuse. The weapon is fitted with a strapdown inertial navigator and in range known modes will fly a range optimising profile. If the target emitter goes off the air, it will search for other threats and attack the highest value emitter to be found. Models including and subsequent to the AGM-88B employ EEPROM (electrically erasable PROM) threat libraries.

The USN’s principal HARM shooters were the F/A-18s, which also comprised a large part of the USMC fixed wing contingent. Smaller numbers of A-7Es and A-6Es also carried the weapon, as did a substantial fraction of the EA-6B Prowler contingent. The F/A-18 installation uses target information from the HARM’s nose mounted seeker and the aircraft’s omni-direc-tional ALR-67 warning receiver, the pilot is provided with a list of targets in descending order of priority displayed on one of the cockpit CRTs, targets are selected with a throttle mounted switch which sequences through the list. The ALR-67 combines both crystal video and superhet receiver hardware and complements the coverage of the HARM, it is however a very basic system in comparison with specialised homing receiver installations such as the USAF APR-38/47 in the F-4G. As such the composite installation provides omnidirectional coverage with low directional accuracy, and forward sector coverage with high directional accuracy due the seeker of the HARM. The most sophisticated USN/USMC installation is that of the EA-6B, which integrates the HARM into the aircraft’s comprehensive ALQ-99 tactical jamming system (see AA 1/89). The EA-6B is equipped with a comprehensive suite of warning and homing receivers and carries specialist operators, this allows highly selective targeting of the HARM against radars and operators which might elude the more basic systems operated by pilots and bombardier/navigators in strike aircraft. This difference in capability is most apparent in a high threat density environment, where the workload associated with selecting and targeting a specific emitter can be excessive for an aircraft with a less capable warning receiver system, and less qualified operator.

The USN’s commitment to fitting aircraft with HARM reflected in workload, with 60% of the total number of SEAD missions flown during the war claimed by the USN, which provided escort jamming and SEAD for many mixed strike packages.

USAF Hard Kill – The F-4G, F-16C and HARM

The USAF deployed its dedicated F-4G Wild Weasel (see AA 7/86) to the Gulf, the lineal descendent of the Vietnam era Weasels. The F-4G carries the APR-47, a sophisticated long range homing receiver system designed to locate, identify and track a wide range of emitters in a signal environ- ment. Using its interferometric antenna systems the APR-47 will pinpoint an emitter with high directional accuracy, while providing continuous real time position data to the HARM missiles carried by the aircraft. The combination of an accurate direction finding receiver with omnidirectional coverage, ranging on emitters and the ability to sort and track a large number of emitters concurrently, with an expert backseat operator provides the F-4G with a uniquely potent capability to selectively target and attack emitters. This capability is enhanced by the ability to feed targeting information to other suitably equipped aircraft.

The F-4G/APR-47 supports HARM in two modes, Pre-Emptive (PE), a range known standoff mode, and Direct Attack (DA) a range known or unknown mode with short reaction time. Both modes support off-axis launches.

Initial deployment saw the 561st TFS of the 35th TFW deploy from George AFB in California to Sheikh Isa in Bahrain, followed by 12 aircraft of the 81st TFS of the 52nd TFW at Spangdahlem, and later a further 12 from the 480th TFS of the 52nd, these attached to the 35th TFW (provisional) to form a composite wing. The 23rd TFS of the 52nd deployed its mixed F-4G/F-16C force to Incirlik in Turkey. In mixed force operations, the F-16Cs, which are fitted for HARM, fly air-air escort for the F-4Gs and carry HARMs to hit prebriefed targets, leaving the difficult mobile targets to the F-4Gs.

The F-4Gs were most active in the first three days of the war, when targets abounded and the Iraqis were not shy about turning on their equipment. At this point in time the Weasels were a designated ‘go/no-go’ item for a strike package, ie no Weasels, no strike. The aircraft concentrated on area defences and point defence SAM systems, with the earlier discussed objectives.

By the end of the first week the Iraqis realised that the SEAD campaign was specifically aimed at eradicating their SAM and GCIEW radar capability and at that point they deliberately shut down as many systems as they could, dismantling and camouflaging many of these to avoid attack, while they also started redeploying their remaining air assets to the North to put them out of the reach of most Allied aircraft.

Once the back of the Iraqi IADS was broken, the Weasel’s tactics shifted toward keeping remaining SAM systems off the air by presence alone, typically a pair of F-4Gs armed with HARM would patrol an area and escort any strike aircraft arriving, then withdraw to refuel from a tanker while another pair took its place. These sorties typically lasted four hours, with short 30 minute escort runs alternating with refuellings. The USAF Weasel squadrons found an increasing fraction of aircraft were returning with unfired HARMS due the lack of emissions to guide on, as a result the aircraft were loaded with bombs, Maverick TV guided missiles and cluster bombs in addition to HARMS. There were two aspects to this decision, one the diminishing level of emitter activity which denied targeting, the other the objective of totally destroying the Iraqis’ capability rather than merely stripping off antennas, allowing a radar to be later repaired or rebuilt. The Weasels’ weapon of choice for suppressing AAA and non-emittingsites was the CBU-87/B Combined Effects Bomblet (CEB) cluster munition. The CBU-87 uses a standard SUU-65/B dispenser (ie bomb body) which has canted tail fins which spin the dispenser up to 2500rpm after release from the aircraft and fin deployment. An FZU-37/B Doppler proximity fuse is typically fitted to provide submunition release at a programmed altitude, the spin of the weapon causes the submunitions to be ejected in a toroidal pattern about the dispenser. The BLU-97/B fin retarded submunitions have a shaped charge, combined with a fragmenting case and incendiary element to cause damage across a broad spectrum of targets.

Of particular interest to the Weasels were SAM launchers and TEL vehicles which, as non-emitting targets, would not attract HARMS as their guidance radars did. These were systematically hunted down and destroyed, where ordnance remained the Weasels expended it against targets of opportunity on the way home.

Toward the end of the campaign emitter activity dropped to zero and many Weasels were retasked with fighter CAP or strike missions, attacking power stations, HAS and other targets. A notable mission was a raid by Maverick firing F-4Gs on the Baiji oil refinery, which left fires active for over a week. In perspective, USAF Weasel operations more than anything resembled those of the Vietnam period, with a return to the idea of complete lethal suppression with a range of munitions (although purists may further argue that the campaign owes more to RAF/USAAF 2ATAF SEAD operations in June, 1944). The Bahrain based 35th TFW flew 2331 sorties for 8587 hours, firing close to 1000 HARMS and two dozen AGM-45 Shrikes.

RAF Hard Kill – The Tornado and ALARM

The RAF’s ARM is the BAE ALARM, a much newer weapon than the American HARM, designed with a much broader range of operating modes. Alarm was designed for SEAD and self-protection of the RAF Tornado, Jaguar and Sea Harrier, al- though at this time it is only carried by suitably modified Tomado GR. 1s.

The Alarm is like the HARM an intelligent autonomous weapon with a wideband homing seeker, unlike HARM it can however loiter and thus is a more suitable weapon for SEAD by non-specialised strike aircraft. Fully programmable in software, the Alarm is best used by 1553B bus equipped aircraft where the fire control or EW system can directly interact with the weapon until launch, if necessary changing the selection of target type and position. The missile receives position updates from the launch aircraft until launch. The Alarm has four principal operating modes.

In Direct Mode the missile is programmed before launch with a prioritised threat file, it is then fired at the target, even from very low altitudes, pops up for its programmed mid-course phase, after which it initiates a search within a pro- grammed box and locks on to the highest priority emitter detected and homes in to impact. Until the missile is committed to terminal homing it will autonomously change its selection of target if a higher value emitter is detected.

In Dual Mode the Alarm will maximise the time during which it can threaten an emitter. If the emitter is radiating the Alarm will attack as in direct mode, if it shuts down, the Alarm will proceed to a point above the emitter where it deploys a parachute and loiters (UK sources indicating a climb to 70,000ft [21,350m]). If the emitter turns on, the parachute is jettisoned and the Alarm dives into the target.

In Loiter Mode the Alarm directly proceeds above the target and deploys its parachute, loitering until the emitter is activated.

In Corridor/Area Suppression Mode the Alarm is fired in the direction of emitters, the position of which may not be precisely known. The missile then autonomously selects the highest priority target for attack. strike package. The USN deployed a total of 27 Prowlers and the Marines 12 (VMAQ-2), with the USAF deploying Ravens from both the 390th and 42nd ECS’ at Taif and Incirlik.

The Ravens and Prowlers provided noise and deception jamming of GCI/EW and acquisition and tracking radars to prevent these from providing targeting information to SAM systems, in addition some Prowlers would have also provided communications jamming against GCI and SAM VHF/UHF communications links using their low band ALQ-149 pods, also effective against low band radars such as the Spoon Rest. As a result, the Iraqi SAM systems were unable to concentrate and coordinate their fire on individual targets, if they could even identify these.

An interesting aspect of support jamming operations was the standoff jamming provided to penetrating F-117A stealth fighters. The commonly held belief that stealth aircraft are invisible to radar is wrong, they are merely less detectable. Similarly the belief that stealth aircraft cannot benefit from jamming is equally wrong (see AA 12/90, 5/87). What a jammer offers is such a reduction in defending radar sensitivity to render an otherwise detectable inbound stealth aircraft effectively invisible, by buryingits return in noise. This was successfully accomplished on a number of raids when support jammers radiated as the F-117As closed on the target, concealing them totally. According to some sources, this practice was later discontinued as it was found that the Iraqis commenced firing blind barrage AAA once jamming was detected, although given the operating altitude of the F-117A this was unlikely to have been an issue.

The only casualty of the campaign was an EF-111A, which impacted the ground while evading a SAM at low level near the Saudi border. Sadly the crew died when the ejection capsule failed.

The EC-130 Compass Call aircraft provided communications jamming of GCI links and command links to SAM and AAA systems, forcing the Iraqis to rely on landlines of substantially lower bandwidth. These aircraft worked long hours, standing off near the boundaries of Iraqi airspace and pouring garbage into Iraq’s airwaves. While not receiving the coverage of the fast jet support jammers, the EC-130s performed a vital role particularly in the early phase of the conflict.

The role of the support jammers in the campaign has been overshadowed by the stunningly successful lethal SEAD campaign, however we must not overlook the fact that the the low aggregate attrition is directly attributable to support jamming, particularly in the early phase of the SEAD campaign when the Iraqis retained sufficient assets to saturate the escorting SEAD aircraft with targets. Any attrition warfare campaign takes time to be effective, ie the results are never instantaneous, and the use of soft kill support jamming provides a most useful buffer by inhibiting hostile air defence capability until attrition reaches a decisive level. The support jamming campaign must therefore be judged as much a success as the SEAD campaign, were it otherwise the attrition figures would be much different.

Defensive Electronic Counter Measures

The final aspect of the three pronged Allied strategy was the application of Defensive ECM (DECM) to protect Allied aircraft from those SAMS which penetrated the jamming and SEAD coverage of the strike packages.

Many of the aircraft deployed in the theatre lacked internal ECM. All USN tactical aircraft carried internal jammers, in most instances the Sanders ALQ-126A or B trackbreakers, supplemented by the ALQ-162 trackbreaker.

The ALQ-126B is a power managed jammer with coverage up to the VJ bands, capable of delivering in excess of 1 kW power per band at 4-5% duty cycles. A trackbreaker designed to defeat pulse mode SAM and AAA radars, the ALQ-126B modes include mainlobe blanking, inverse con-scan, range-gate pull-off and swept square wave which make it particularly potent against established Soviet conically scanning systems such as the SA-6/Straight Flush tracking/illuminating radar or the ZSU- 23-4P/Gun Dish fire control radar. The 126B installation typi- cally uses fore and aft antennas with 60 degree beamwidth and 15 degree depression to cover surface threats. On many aircraft the 126 is supplemented by the ALQ-162 which is a specialised continuous wave (CW) trackbreaker designed to defeat devices such as the SA-6 missile SARH seeker.

All USN/USMC tactical aircraft carried internal warning receivers, in all instances either the standard ALR-67 or in older aircraft, the ALR-45 and 45F. These receivers are systems which combine crystal video receivers, superhets and a low band receiver. Four cavity backed spiral antennas are used for threat direction finding. Some older aircraft have an additional APR-43 Compass Sail/Clockwise C/D band launch warning receiver, which intercepts and analyses the command uplink signals associated with SAMs such as the SA-2, SA-3 and SA-6. The substantial dependence of Soviet SAMs upon command uplinks and tracking beacons (see table Part 1) makes for unambiguous indication of the state of the engagement.

The USN’s attention to DECM in tactical aircraft was not matched by the USAF. Of the USAF’s tactical inventory, only the long range F-111 and F-15 carried internal trackbreakers. The F-15C and E carried derivatives of the basic ALQ-135 TEWS, a capable system with high band coverage, of which little has been published in open sources. The F/EF-111A/E/F carried various models of the ALQ-94/137, a combined pulse mode and CW deception and noise jammer with three subsystems covering low (E/F), mid (G/H) and high (I/J) bands with fore and in some airframes, aft coverage.

The F-168, F-4Gs, RF-4Cs and A-10s lacked internal jammers, the F-16C in particular missing out on the planned upgrade to the internal joint service ALQ-165 ASPJ. This created much heartache for the USAF, which was left with the task of distributing its meagre stocks of podded jammers amongst the close to 1000 aircraft. Of the newest type, the ALQ-131 Block 2, only 260 were available, supplemented by 130 older model Block 1 pods which required pilot selection of jamming mode. In addition to the 131s, the USAF also had 250 older ALQ-119s and 50 Vietnam era ALQ-101s, many of which probably saw action over Hanoi. The F-4Gs were fitted with Raytheon ALQ-184s, which are upgraded from ALQ-119s.

This situation created much pressure on the SEAD and support jamming forces, particularly since only the 131 and 184 could cope with newerthreats, thus leaving the F-16s and A-10s otherwise susceptible to fire from weapons such as the SA-6 and SA-8 or Roland. Fortunately, the MTBF of the newer pods was exemplary, the 131 demonstrating 180hrs (ie four times. design spec) between failures, thus allowing for little downtime due pod outages.

The Westinghouse ALQ-131(V) is the USAF’s standard jamming pod, evolved from the earlier ALQ-119(V), in turn evolved from the Vietnam era ALQ-101 and QRC-335 programmes. The 131 is designed as a fully modular system, with fully self contained cooling and support functions. The system is built around a C/I (Control/Interface) module which contains a digital computer and a programmable digital waveform gen- erator, the latter feeding an array of jammer modules. The system can be slaved to an aircraft’s RWR or controlled by an internal power management module, and is reported to provide a range of noise and deception jamming modes.

Raytheon’s ALQ-184(V) is a relative newcomer also derived from the ALQ-119 family. It employs Rotman lense antennas and provides noise and deception jamming modes, in the latter operating as a deception repeater.

USAF radar warning assets were no less diverse than their DECM assets. Older tactical aircraft such as the F-4 and A-10 carried versions of the standard ALR-46 family, capable of handling up to 16 threat emitters concurrently, typically supplemented by a C/D low band ALR-64 Compass Sail launch warning system. The ALR-46 is a conventional crystal video receiver with a quartet of cavity backed spiral antennas for direction finding. The F-16s carried the ALR-69 which is an enhanced ALR-46 with integrated Compass Sail equipment, and a frequency selective receiver set, the latter capable of analysing guidance transmissions to determine the direction from which the missile is approaching, The F-111s and F-15s carried type specific warning equipment. The F-15C/E carried the capable E-J band ALR-56C, a dual conversion H/I/J band superhet receiver, supplemented by an ALQ-128 countermeasures receiver, whereas the F-111E/F carried the third generation of the C-J band ALR-62 warning and homing system, the current incarnation including an in- stantaneous frequency measurement receiver for precision direction finding. The EF-111A carried a modified subtype, the ALR-62(V)4 with facilities to ‘look through’ jamming by the ALQ-99Ė.

Insofar as can be established from open sources, the USAF and USN diverge substantially in their respective strategies for the design of DECM systems, the Navy concentrating on specific trackbreaking techniques designed to defeat fire control systems, whereas the Air Force places a greater emphasis on generic techniques for defeating acquisition and fire control radars. While this more than anything reflects the differences between the naval environment and air-land battle environment, it has the benefit of presenting an opponent with a diverse array of jamming techniques to cope with.

In the Gulf this effect was further enhanced by the presence of the RAF, who employed their own unique DECM equipment. The Tornado GR. 1 carried an internal Marconi Radar Homing and Warning Receiver (RHWR) for threat detection, and the Skyshadow deception jamming pod. The RHWR covers the C to J bands, and will identify and classify AI radars, SAM and AAA acquisition and tracking radars and missile guidance emissions. The system provides long range warning and homing which implies the use of superheterodyne receivers. The Skyshadow trackbreaker pod will concurrently counter pulse mode and continuous wave emitters with angle and range denial techniques, and will automatically prioritise threats and select appropriate jamming techniques and power levels.

In addition, radar absorbent tiles were attached to the inlets to provide a useful reduction in frontal radar cross section, to enhance the effect of the Skyshadow’s jamming when closing on a target. The RAF’s Jaguars carried the older ALQ-101-10 jamming pods in addition to an internal RWR. The RAF expended much effort, like the Americans, in the prewar period to ensure that the threat libraries in the jammers were up to date. The mix of very old and very new Soviet built equipment, supplemented by Western equipment, and the unplanned for high/medium altitude operational environment, resulted in much software development effort to ensure that all threats were covered.

The Allied DECM effort was greatly assisted by the fact, that all of the threat systems in the theatre were well known (see Part 1), although in hindsight this would have also been true of a Warpac/NATO conflict, as the Soviets were unlikely to have deployed the new SA-10, SA-11 and SA-12 in strength to the front line for fear of compromising them to Allied Elint. The low aggregate loss rate testifies to the effectiveness of the equipment, as most launched SAMs went ballistic even when guided.

The Allied DECM effort was greatly assisted by the fact that all of the threat systems in the theatre were well known (refer Part I), although in hindsight this would have also been true of a Warpac/NATO conflict, as the Soviets were unlikely to have deployed the new SA-10, SA-11 and SA-12 in strength to the frontline for fear of compromising them to Allied Elint. The low aggregate loss rate testifies to the effectiveness of the equipment, as most launched SAMs went ballistic even when guided.

The success of the Allied electronic combat campaign is a direct result of both careful and comprehensive planning, and the high operational standard of the aircrew operating the equipment. There can be no doubt that the Iraqis lost the air war primarily due to their inability to deal with the Allies’ electronic assault, which effectively crippled their air capability in a matter of hours. It is also fair to say that the Iraqis lost the war in the first hour and then took six weeks to realise that the obvious.

The central message to be derived from Desert Storm is that command of the air in this modern age requires as a prerequisite command of the electromagnetic spectrum. Whilst this may have been evident to expert observers for some years, it has taken a substantial air war to demonstrate this conclusively.

The message for the future is equally clear, if you lose the electronic battle, you lose the air battle, if you lose the air battle, you lose the war. If you wish to prevail in a modern air war, you must take electronic combat seriously. Those who do not will be without doubt tomorrow’s losers.

Part IV discusses specific lessons for the ADF.

References

1 Luti, WJ, Battle of the Airwaves, USNI Proceedings, 1/1992.

2 Hampton, D, Combat Defence Suppression, Journal of Electronic Defence, 10/91.

3. International Counter Measures Handbook, Cardiff Publishing, 1989, 1991.