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The story of Downtown is the story of a revolution in tactics and technology. The air campaign over North Vietnam was not like any battle before (or arguably, since). Technology transformed the fighting and tactics had to catch up. The US and Vietnamese started Operation Rolling Thunder in 1965 with weapons and doctrine unchanged from WW2 and Korea. By the end of Operation Linebacker in 1972 the US and Vietnam's Russian backers had perfected the weapons of the Gulf War.
Downtown illustrates this revolution.
Nowhere was the revolution so profound as in the changes in weapons and tactics for ground attacks. The US military of the early '60s was built around the delivery of nuclear weapons. Strategic Air Command (SAC) had hoovered up much of the resource for this mission while its Cinderella sister, USAF Tactical Air Command (TAC), was left trying to find a role.
When Rolling Thunder came along the requirement for precision conventional bombing pushed TAC to the fore. But it wasn't equipped for the job. The workhorse F-105 Thunderchief had a radar bombsight that could drop a nuke within a city block of its aim point but was useless for placing high explosive precisely on a bridge span. Experiments were made during Operation Northscope and Operation Commando Nail to develop precision radar attacks with specially trained F-105 crews (codenamed 'Ryan's Raiders'), but their results were disappointing.
For attacks on point targets like bridges, the only option was daylight dive-bombing attacks over open sights. This was a mode of attack indistinguishable from WW2 or Korea, except the Air Force was doing this with supersonic jets. In spite of some brave and skilful work by Air Force pilots, they just didn't have the accuracy, particularly under intense anti-aircraft fire, to guarantee destruction of the target.
An EB-66 leads F-105s on a pathfinder radar bombing mission
The primary weapon for attack was the high explosive bomb: initially of Korean vintage, though a new generation of aerodynamic 'slick' bombs were later used. Some had retarding devices in the tail to allow low-level release and others had fuses on extender devices to allow airbursts rather than ground bursts. 500lb and 750lb weapons were most common, though special targets such as the great Hanoi bridges -- the Paul Doumer and Canal des Rapides -- could require bombs up to 2,000lb or 3,000lb in size.
The unguided rocket was a popular supplement to the 'dumb' bomb, often used by Navy aircraft on route reconnaissance. The Cluster Bomb Unit (CBU) also began to make itself felt. This was a popular and effective weapon for suppressing anti-aircraft gun sites and SAM batteries. However, accuracy with weapons declined as the density of flak in North Vietnam increased. Climbing casualty rates forced the bombers higher and higher, with a profound effect on their accuracy. Pullout heights of 2-3,000 feet were too hot for fighter-bombers and by the end of Rolling Thunder aircraft were commonly pulling out of bombing runs at 8,000 feet or higher.
The key measure of accuracy was the Circular Error Probable (CEP), the distance from the aim point inside which half the bombs would fall. CEPs for attacks from higher altitudes were a whopping 500 feet or more, which was barely enough for beating up an area target like a rail yard, let alone knocking out a 40 foot-wide bridge. The story of Rolling Thunder is one of key targets that refused to die and had to be struck and restruck again, and of bombs that would often go astray, killing civilians.
The US Navy, unhampered by TAC's nuclear doctrine, had similar problems in placing bombs on targets. Their secret weapon was the introduction of new aircraft types such as the A-6 Intruder, with an excellent radar bombsight capable of hitting smaller targets, though it still had problems achieving pinpoint accuracy. The later versions of the A-7 Corsair had one of the earliest Heads Up Displays with a CCIP (Continuously Calculated Impact Point) aiming dot which aided visual aiming. In Linebacker A-7s were able to reduce CEPs to around 33 feet -- a quantum leap in accuracy but still too late for Rolling Thunder.
There was a further problem for the air attackers: the weather. The monsoon cycles over North Vietnam meant that half the year visual bombing was impossible because of thick, low cloud. Bombing would slack off from November to April because the targets were nigh invisible.
Attempts were made to get around this. 'Ryans Raiders' and other radar-bombing schemes were one. Another was the use of radio navigation fixing, where aircraft would drop bombs based on radio fixes from ground stations in a fashion similar to the X-Gerat and Oboe systems of World War 2. Combat Skyspot was an updated version of these systems and had achieved some successes near the Demilitarized Zone between North and South Vietnam. But the Red River region was so far away from US airbases that forward radio beacons were needed to aid the bombing. The most famous of these was site Lima 85 on the mountain Phou Pha Thi in Laos, manned by the CIA and finally overrun by the Communists during a tragic incident in which evacuation was ordered too late. The tragedy was compound by the futility of the effort. Combat Skyspot was so inaccurate that a post-war study showed the campaign -- codenamed Command Club -- was worthless, achieving nothing for great loss of life and earning the title "Commando Kaze" from the pilots.
Walleye II glide bomb
The US bombing of the Red River region ended in 1968. Jets wouldn't drop ordnance there again until 1972. But the end of Rolling Thunder saw the beginnings of the revolution. The first guided weapons had been developed by the Navy. Early versions of these were missiles like Bullpup which had to be guided by a crude command system and were not that effective. But in 1967 the first TV-guided bomb, named Walleye, appeared. Walleye would lock-on to an image (say, of a bridge) and then guide on it. CEPs with the weapon were in the region of 10-20 feet.
Early use of Walleye had some notable successes, such as against the Sam Son barracks where a bomb entered through a window and blew the building apart. However, the Walleye was a temperamental weapon; effective where there was good visual contrast but losing reliability if weather was overcast or if dust (say from previous explosions) obscured the target. It also suffered from having too small a warhead. Its 825 lb of high-explosive lacked the punch to knock out concrete and steel bridge supports.
It wasn't until 1972 that the larger Walleye II entered service. Its 1,900lb HE warhead was hefty enough to take down the infamous "Dragon's Jaw" bridge at Thanh Hoa -- an overengineered monstrosity that had withstood years of pounding from the air but succumbed to a single strike with the new Walleye weapon. Walleye offered the Navy and Air Force another new capability: the ability to standoff from the target. These were glide bombs with a range of over five miles. Jets could launch them from outside the lethal envelope of flak.
Paveway I series bombs
But by 1972 there was another precision-guided weapon that had matured beyond the capabilities of the TV bomb. Laser-guided weapons had made their debut over Laos. By the time the USAF and Navy returned to the Red River in Operation Linebacker the technology was proven and delivery techniques perfected. Laser Guided Bombs (LGB) were codenamed Paveway and were conversions of conventional bombs which involved strapping on a guidance nose and steerable tail fins. In their earliest form a small laser designation gun was placed in the back seat of a Phantom jet. While the Phantom orbited the target, the backseat crewman would guide the beam of his 'Zot Box' at the target and the backscatter from the beam would form a cone -- a 'basket' for bombs to be dropped in. Accuracy was phenomenal, with CEPs of sub-10 feet.
Pave Knife designator pod
For Operation Linebacker the 'Zot Box' was replaced by a massive underwing laser-guidance pod named Pave Knife. This pod, with its ability to designate the target from different angles, released the Phantom jet from the requirement to orbit the target. However, the pods were precious and General Vogt of the US 7th Air Force joked that any pilot who accidentally lost a pod had better never come back alive. Vogt's strategy was to protect the pod and their carrying aircraft by launching massive protection forces to accompany the strikes.
This graphic shows the protection for Rolling Thunder and Linebacker-era strikes. Note the increase in support forces to defend fewer bombers
The new precision-guided munitions were not a panacea. They were still nullified by bad weather as before, while dust and debris from early strikes could spoof them. But in the brief patches of clear weather the Air Force and Navy now had a true one-bomb one-kill capability. This meant fewer strikes could destroy more targets in quicker time for less loss of civilian life. The accelerated bombing campaigns that became a staple of the Gulf, Serbian and Afghan adventures, were now possible.
Herman Gilsters's classic post-war study of Linebacker II put the revolution in weapons accuracy into perspective. Comparing LGB with radio navigation (LORAN) bombing with radar guided bombing and conventional visual dive-bomb attacks, he discovered that they generated the following relative effectiveness factors:
LORAN effectiveness = 0
Radar Bombing effectiveness = 1
Visual Bombing effectiveness = 8
Laser Guided Bombing effectiveness = 124
In essence, laser guidance was 16 times more effective than dive-bombing and 124 times more effective than radar bombing. The revolution was complete.
(Figures taken from The Air War in Southeast Asia: Case Studies of Selected Campaigns by Herman L. Gilster, Air University Press 1993)
An S-75 (SA-2) missile on its launcher
The introduction of the Surface-to-Air Missile (SAM) had a profound impact on the war over the Red River delta. The Vietnamese had been supplied with an off-the-shelf Soviet missile system, the S-75 Dvina, which NATO had codenamed "SA-2 Guideline". The missile was a massive two-stage weapon, designed for hitting stratospheric targets like U-2 spy 'planes. A giant booster would accelerate to supersonic speeds and then hurl the dart-like upper stage at a target. Recieving steering commands from its radar ground station the upper stage would home on its target and explode when in proximity. The huge HE-fragmentation warhead could swat down fighters 200 feet from the detonation point and severely damage them up to 350 feet away.
The Vietnamese deployed SAM battalion units of six missile launchers, serviced by radar and control vans. They prepared a number of special sites with telephone or radio connections to air defense command. From these camouflaged positions they could search out targets with their early warning radar or have targets allocated to them by air defense command. They would then acquire the target using the battalion's 'Fan Song' guidance radar before launching.
A Fan Song radar van. Note the small hut on the top of the radar. This station could be used for optical-guidance control of the missile in a jamming-heavy environment
The first SAM shootdowns in the summer of 1965 goaded a severe reaction from the US. While the SAM sites were being built they had been off-limits to air attacks for fear of killing Soviet advisors and escalating the war. But when the sites went live, the White House gave immediate clearance to attack them. The first such raid was on 27 July 1965. USAF jets hammered a SAM crew barracks and a SAM site near the Black River, only to run into flak traps set by the Vietnamese. The Air Force lost four aircraft. Worse, their attacks had no effect since the SAM sites were either empty or contained carefully-made dummies.
Early strikes such as this showed the futility of going after the SAMs directly. The Vietnamese could move their battalions quickly from site-to-site. With some twenty to thirty SAM battalions shuffling between dozens and later hundreds of sites scattered across the countryside they could play a sophisticated 'shell game' with the Americans. The Vietnamese built dummies to fool photo-recon 'planes and could fake radar emanations to foil electronic listening. Even if the Americans did get a positive fix, taking on the well-defended SAMs mano-a-mano usually cost more than it gained. Quickly, the emphasis changed from destroying the SAMs to suppression and threat reduction.
To reduce the threat an 'electron war' was fought in the skies above Hanoi. The Communist air defense system was based on a massive network of radars: early warning radars to detect raids far away; SAM radars to acquire targets and guide missiles; and gun-laying radars such as the Fire Can for anti-aircraft artillery (AAA) units. This radar threat would need to be defeated by American know-how.
A pair of EB-66 jamming aircraft of the 355th Tactical Reconnaissance Wing
Both the Air Force and Navy operated electronic warfare aircraft. These could stand off at a distance in a 'racetrack' orbit. They would watch enemy radars light up, then jam them with powerful broadcast beams. US tactics were to place the jamming aircraft directly behind the path of the raid. When the radars lit up to engage the raiders they would face right into the jammers where the jamming beams had the greatest effect. If the radar pointed away from the jammers, so as to engage aircraft coming from a different direction, then the jamming beams would feed into the radar 'side lobes' where they'd have significantly less effect.
The first panel shows an EB-66 jamming aircraft broadcasting a jamming beam at a 'Bar Lock' early warning radar. The second panel shows the main radar beam (in blue) pointing at the incoming raid with the 'side lobe' broadcasts (in orange). Note the EB-66 is positioned to broadcast jamming right down the main beam. The final panel shows the radar tracking a raid coming from a different direction. The EB-66 is no longer positioned within the main beam and the best it can hope for is to try and feed interference into the radar's secondary 'side lobes'.
The jamming mission was further complicated by the square law that causes a jammer's broadcast power to slack off with range. Beyond a certain distance, jamming was worthless. As the war went on the Vietnamese did their best to discourage jammers from getting too close, often by sending out MiGs to intercept. The Air Force's jammers were pushed back further and further until their influence over the battle was limited.
Standoff jammers were not the total answer to the SAM and Fire Can threat, then. What was needed were electronic systems that protected the aircraft directly. There were two parts to solving this problem. The first was the need to warn aircraft when they were being tracked so they could take action. The second was direct protection.
The first Radar Warning Recievers (RWRs) began to appear in 1966. These devices had a scope readout bolted inside the cockpit that could display the bearing, strength and type of radar beam strobing the aircraft. RWRs were lifesavers, often directing a pilot's attention toward a SAM launch in time to do something about it.
The S-75 SAM was designed to tackle unmaneuverable bombers and spy 'planes, not nimble fighter jets. Pilots soon discovered they could outmaneuver the missile. They developed a technique known as the "orthogonal roll" as a last-ditch defense. Timed correctly, a roll and dive would put a missile in a position where it couldn't track its target without having to turn a square corner, at which point it would sail past and miss.
Another SAM avoidance technique was for aircraft to go low 'in the weeds' and use terrain to mask them from the SAM radars. This was more dangerous because it put the aircraft in range of flak. What was needed was a magic box that could block missile attacks without the need for avoidance maneuvers; a jammer carried aboard the aircraft.
Predictably, the US Air Force and Navy went their separate ways on finding a jamming solution. The Navy were early adopters of deceptive jamming systems. These were black boxes capable of deceiving radars as to the range of an aircraft. 'Project Shoehorn' worked to try and fit all Navy aircraft in-theater with these jamming systems. Though the program started in late 1965, the first carrier wing to benefit from Shoehorn (CVW-15 aboard USS Constellation) did not arrive on-line in theater until mid-1966.
Two F-105 Thunderchiefs hauling loads of 750lb bombs to targets in North Vietnam. Note the nearer 'Thud' is carrying a QRC-160 jamming pod on the outer pylon. By the end of 1966 this was a standard fitting on USAF fighter-bombers.
The Air Force took more convincing. Attempts were made to encourage the USAF to adopt an underwing noise jamming 'pod' named QRC-160, built under a 'quick response' contract. For pilots and wing commanders there was a distinct "not invented here" attitude to the pods, at a time when casualties to SAMs and ground fire were horrendous. However, when trials in late 1966 caused casualty rates amongst fighter-bombers to plummet there was an overnight change of heart. Indifference to jamming pods evaporated. Attack pilots now demanded them, resulting in a brief pod shortage. The shortage meant that escort fighters had to wait until the following year to get their pods and for a while casualties remained high amongst the fighters.
Where jamming worked, it was very effective. The noise jamming QRC-160 pods would fill the enemy radar scopes with strobe lines that made it difficult to fix targets. However, the pods started to place all sorts of restrictions on the raiders. The USAF pods broadcast jamming into a cone beneath the aircraft so that hard maneuvers would point the cone away from SAMs and make the 'plane a clear, hard target in the sky. The pods worked best when aircraft flew in a specially-spaced formation that would create a 'zone of uncertainty' around them. This made SAMs more likely to miss. Formation discipline and careful flying became paramount.
It was then discovered that placing all the bombers into a special 'jamming cell' formation made the jamming even more effective. The jamming cell was more vulnerable to MiG attack because of the close flying it required, but was very efficient against SAMs.
This illustration shows a typical line-abreast jamming cell formation used by the 388th Tactical Fighter Wing in Operation Rolling Thunder. SAMs would tend to aim for the space between the four flights of aircraft and explode harmlessly. Variants on this formation included a staggered version and a five-flight "star gaggle" formation.
The problem came when the bombers had to break formation so as to bomb their targets. At this point they were vulnerable to radar-directed attacks. What's more, at very close ranges SAM radars were powerful enough to 'burn through' any amount of jamming, stripping the layers of electronic protection from the target.
A game of move and countermove was being played out in the electronic arena. Periodically the Vietnamese would alter their radar frequencies to try and degrade the effects of jamming. The US had to adjust their jammers to match the new frequencies. Then in 1968 a new and quite effective form of American jamming appeared. This directly attacked the 'beacon frequency' that controlled the missiles in flight. Beacon jamming would send SAMs completely haywire.
In the spring of 1972 Operation Linebacker opened. To protect vulnerable figher-bomber formations trying penetrate the Hanoi defenses, General Vogt, commander 7th Air Force, added a new layer of protection to his raid packages.
'Chaff' was the name for clouds of small dipoles made from precisely cut lengths of metallized fiberglass. Dropped by airburst bombs or dispensed from special pods, eight aircraft could lay a 'chaff corridor' five miles wide by 30 or 100 miles like a carpet. Aircraft flying in or just above the layer of chaff were masked from radar beams in the fifteen-minute window before the chaff dispersed. With standoff jammers, jamming pods, beacon jamming and chaff combined, raids were largely safe from the ground defenses.
Chaff was so effective that the Vietnamese MiGs started to attack the chaff-laying flights and escort protection for them became a priority. The chaffers had several strategies, including laying a chaff corridor down in front of the following strike package or flying to the target and laying the corridor back from there to the strike. Alternatively they would split and lay inbound to and outbound from the target simultaneously. Escort tactics for the chaffers also varied. they could close-escort the chaffers or set up a patrol barrier against MiGs near the target.
This illustration shows the different methods of chaff delivery. Laying a corridor outbound to the target; laying it inbound; laying outbound and inbound simultaneously. The chaff took about 10 minutes to form a cloud large enough to affect radar, then another fifteen minutes before it dissipated. So co-ordination between the strike and chaffers was critical.
Attempts to nail the SAMs with air strikes in Operation Rolling Thunder had largely failed. The Vietnamese were too good at hiding their SAM sites and would only reveal them when the opportunity for a shot presented itself. What was needed was a force to hunt out the SAMs when they exposed themselves. These elite, specially-equipped units would escort the strikes in and either blast the SAMs or try and harry them so they wouldn't interfere with the strike.
This new mission went by many names. 'Iron Hand' was one codename. 'Suppression of Enemy Air Defenses' (SEAD) was the acronym. The Air Force called their SEAD units 'Wild Weasels' and their exploits were legendary. In addition to SAMs, their mission was to neutralize AAA near the target, including the AAA-directing radars such as Fire Can.
F-100F Wild Weasel I fighter-bomber
Early experiments with the Wild Weasel concept set the pattern. The first Weasels were two-seat F-100 fighter-bombers. The pilot would fly and fight while the backseater, or 'Bear', would operate the radar warning electronics sniffing out the enemy signals and provide an extra pair of eyes. Early weapons loads for the Weasels included rockets and bombs. However, these all required the aircraft to close to point-blank range with the enemy. Legend has it that the first commander briefed on the mission responded "You gotta be sh--ting me!". The phrase became emblematic of the Weasels' daring and élan.
The experiment with F-100s was brief, and it was soon replaced by the F-105F Wild Weasel III. This still carried bombs: often cluster weapons for scattering over lightly-protected AAA and SAM, but it also had a new longer-ranged weapon, the AGM-45 Shrike.
The Shrike AGM-78 anti-radiation missile
The Shrike was originally a Navy weapon, used by A-4 Skyhawks in the Iron Hand role. It was an Anti-Radiation Missile (ARM) that possessed a radar homing seeker in its nose. If the enemy lit up a SAM or Fire Can radar, the missile could be launched and would guide at the radar antenna. If it hit its small fragmentation warhead would shred the antenna, putting the radar off-air. Without radar there was no guidance and no threat.
The Shrike wasn't a panacea weapon. Its range was not all that long, requiring aircraft to get well within the reach of the SAMs before launching. Range could be extended by 'lofting', or tossing the missile from a distance, though this reduced the chance of a hit. Most importantly, if the radar shut off before the missile could hit, it would lose its homing signal and miss. Metals in the Shrike's rocket motor made a distinct radar signature when a missile launched, warning SAM batteries that an ARM was on the way. Also the Vietnamese monitored the American radio net; the codeword 'Magnum', signifying an ARM launch, could be enough to cause radar operators to flick the 'off' switch.
The Shrike was not easy to use. The missile had to be pointed right at the target to guide, requiring a good fix on the radar. Its warhead was so tiny that the damage caused could be easily patched up. To this end a bomb load was often necessary to finish the target off. Later Shrikes were equipped with target-marking smoke to locate the radar for a follow-up attack.
In the Air Force the Weasels were in short supply, so the usual complement of aircraft for a strike were two elements of two aircraft working as a team. In the Navy two flights of Iron Hand were usually backed by two further flights carrying bombs or rockets in support. The Iron Hand motto was "first in, last out". They would arrive early and orbit the target area, waiting for enemies to reveal themselves. They'd then protect the strike raid as it passed through and cover its departure. Success was not measured by kills against SAM sites, but by whether the mission was able to be completed without the loss of American aircraft.
The result was a cat-and-mouse game between the SAMs and Iron Hand. SAMs that stayed on air too long would recieve a Shrike, so the Vietnamese would bring their SAMs on-line for as brief a time as possible: just long enough to acquire an enemy and attack with a SAM. The Iron Hand mission tended to be highly risky. The aircraft often flew quite low, exposing themselves to AAA. In the case of the Air Force Weasels they couldn't use jamming protection because it interfered with their detection gear.
AGM-78 Standard anti-radiation missile (bottom). Note the size comparison with the smaller Shrike (top left)
After Rolling Thunder new aircraft and weapons joined the Iron Hand mission. The Navy introduced the A-6B Intruder which could carry a new Anti-Radiation Missile: the AGM-78 Standard. Standard had a much bigger warhead and more advanced seeker than the Shrike. It could be fired at enemies off the aircraft's nose, and had a 'memory' function so that if the target radar shut down the missile would continue to guide to the last known location. The weapon's size and expense meant it was used alongside the smaller, cheaper Shrike. The A-6B had some advanced gear for the radar-hunting mission that the Air Force didn't possess such as Passive Angle Tracking via ARM (PAT-ARM), which used the Standard missile's seeker to triangulate on enemy radar emissions.
The Air Force's new aircraft was the F-105G -- the definitive Vietnam Wild Weasel. This had new electronics and also carried the Standard. However, it had given up its bomb load. To make up for this, in Linebacker the Weasels began to operate in hunter-killer teams with F-4E Phantoms. The Weasels carried ARMs and the Phantoms hauled cluster bombs to finish targets off. This turned into a very profitable arrangement.
Without Iron Hand, casualties over North Vietnam would probably have been unsustainable. Development of these tactics were a necessary counter to radar-guided defences. Lessons learned in Vietnam would again be applied almost 20 years later to keep the Iraqi air defences firmly muzzled.
Air combat in Vietnam was, like bombing, a product of new and maturing technologies. The gun weapon of WW2 and Korea had largely been replaced by the air-to-air missile and great store had been placed in the new guided weapons. However, performance was less than expected.
For the US the most effective killer was the Navy-developed AIM-9 Sidewinder missile. This simple boost-coast guided rocket homed in on the infrared (IR) radiation from the jetpipes of enemy aircraft. The AIM-9B initial production version saw service in the USAF and USN for much of Rolling Thunder, but the missile achieved very poor kill rates, with 29 kills off 187 launches, with 53 misses and 105 weapon failures.
This low 0.15 probability of kill (pK) came about for a number of reasons. The weapon needed to see the target's jetpipes to home, requiring attacks from with the 'launch envelope' - a cone astern of the target. If the target turned it could mask the infrared source for the guidance system, shrinking the launch envelope to nothing. The infrared seeker could also be masked by clouds or decoyed by the IR radiation from cloud or the ground. The weapon's flight performance was affected by air density so that an AIM-9B at high altitude had a range just under three miles which shrank to around a mile at very low altitude.
Maintenance problems, ground handling and the harsh Southeast Asian climate also contributed to malfunctions, but one of the primary reasons for poor missile performance was inadequate training in their use. It was found that pilots frequently fired their missiles outside the launch envelope. Studies concluded that improved training was needed, better indication of when a target was within the launch envelope, and that missiles with larger launch envelopes were required.
At this point the USAF and USN forked their Sidewinder development, with the Navy ordering the AIM-9D and the Air Force ordering the AIM-9E. The split was a result of petty service rivalry and disagreements over the type of infrared seeker to be used. It resulted in different cooling mechanisms for the seekers which in turn meant different launch rails for carrying Air Force and Navy missiles. Neither service would be able to use the other's missiles.
The USAF's AIM-9E proved to be a tremendous disappointment. Despite changes to improve 'dogfight' performance its results in the field were worse than the AIM-9B, achieving a probability of kill (pK) of just 0.08 in 1972. By comparison the Navy AIM-9D was a great success. With a better seeker and aerodynamic improvements it had a longer range and larger launch envelope than the AIM-9B. In Rolling Thunder it would achieve a pK of 0.18 and later it would beget the superior AIM-9G and H variants. The Navy also instituted a new, realistic training program focussed on its 'Top Gun' weapons school. In 1972 the combination of training and weapons improvements resulted in the AIM-9G achieving a stunning pK of 0.46.
The Air Force made little attempt to improve air combat training training. Searching for a technological solution to the problem it would make one last attempt to improve its Sidewinders in Vietnam with the AIM-9J. However, inadequate testing failed to detect design faults that crippled the missile when deployed in the field. In 1972 the AIM-9J would achieve a probability of kill (pK) of just 0.13. After the war the faults would be rectified and the missile made comparable with the Navy Sidewinders, but the improvement would come too late.
The Sidewinder's rival infrared missile in Vietnam was the Hughes-made Falcon AIM-4D. This small, complex Air Force missile was introduced to the theater in May 1967 and quickly proved itself a lemon. The long arming and launch sequence, lack of a proximity fuze, tiny warhead and terrible reliability all added up to a miserly 0.09 probability of kill, and soon AIM-4D-armed Phantoms were being switched back to the Sidewinder.
Many USAF Phantom pilots complained about the lack of a gun on their F-4C and F-4D aircraft. Arming restrictions meant their missiles had a minimum range within which close enemies could not be hit and it was widely believed that many DRV MiGs got away when the presence of a gun could have killed them. F-105s had 20mm Vulcan cannon built in and had some successes against MiGs that had tried to tangle with them.
Air Force lobbying for a gun in the Phantom would eventually result in the F-4E with a Vulcan cannon. As a stop gap in Rolling Thunder from May 1967 some F-4Cs and F-4D began to carry a Vulcan in a centerline gun pod and quickly began to claim successes. In Rolling Thunder, where guns were used in conjunction with lead computing gunsights they were able to achieve a probability of kill (pK) just over 0.16.
Air Force myth has it that the addition of the gun to the Phantom was a validation of the old gun concept and that it had been wrong to ditch the weapon from the new generation of fighters. However, the missile - particularly the AIM-9 Sidewider - was still the biggest killer in Vietnam. In the Linebacker campaigns of 1972 the Navy - with a fighter force entirely of Phantoms with no gun capability - achieved twice the number of kills per engagement than the Air Force achieved. The restoration of the gun was not quite the clear-cut panacea of Air Force legend.
The Phantom carried another weapon in its arsenal - the radar-guided AIM-7 Sparrow. Designed for attacking bombers during radar interceptions it had difficulties against small maneuvering MiGs. The Sparrow was supposed to be used 'Beyond Visual Range' (BVR), but BVR shots were often prohibited by rules of engagement designed to prevent 'blue-on-blue' attacks on friendly forces in the crowded skies over North Vietnam. Eventually, tactics were adopted that eased the rules of engagement, while technology such as the USAF's 'Combat Tree' Identification Friend-Foe interrogator allowed them to be relaxed further. However, the restrictions prevented the weapon from being employed to its full extent.
Unlike the Sidewinder the Sparrow was not restricted to stern attacks only, but in close-in dogfights the missile found it difficult to catch maneuvering targets. A large minimum range contributed to this problem, which was exacerbated by the need of the launch aircraft to keep the target 'painted' with its radar so that the missile would guide. At low altitudes radar reflections from the ground reduced the chance of a successful attack, and the complexity of the delicate radar weapon made it unreliable. Overall probability of kill (pK) in Rolling Thunder was just 0.08.
The early AIM-7C Sparrow had soon given way to the ubiquitous AIM-7E. While the Navy came to rely on their excellent Sidewinder missiles, the Air Force tried to soldier on with the Sparrow. The AIM-7E-2 'Dogfight Sparrow' was introduced which cut the missile's minimum range and improved launch times. The result was that in Linebacker the Air Force used Sparrow in preference to the gun and Sidewinder, bagging 30 of their 48 kills in that campaign with the radar weapon.
The DRV's MiG-17 force exclusively used cannon in air-to-air combat. The battery of 37mm and two 23mm cannon were slow-firing but enormously powerful; just one hit from the 37mm would take most American fighters apart. There were rumours of MiG-17s being equipped with air-to-air missiles but there appears to be no evidence to back this claim.
The Vietnamese MiG-19s (and their Chinese-built copies, the J-6) also had a battery of three 30mm guns. Attempts were made very late in 1972 to equip the MiG-19 with missiles but this version never saw combat.
The MiG-21 force was initially equipped with a single 30mm cannon and R-3S missiles. The R-3S, codenamed 'AA-2 Atoll' by NATO, was essentially a copy of the Sidewinder. Stories of how the copy came about vary from reverse-engineering captured missiles to Swedish spies, but it was almost identical in form, function and performance to the AIM-9B and is believed to have near-identical probability of kill (pK) - around 0.13. It took a while for the Vietnamese Air Force to learn to use the weapon. In its early days they were so frustrated with its performance that for a short while they took to equipping a MiG's wingman with unguided rocket pods in case the missiles failed.
Eventually the missile became the mainstay weapon of the MiG-21. Much to the pilots' disgust many newer versions of the aircraft were equipped with no gun at all and cannon didn't return until the adoption of the MiG-21MF in the '70s.
Downtown copyright Lee Brimmicombe-Wood, 2001-2016. All rights reserved.