The three specially-modified UMA were deployed to Vietnam under Operation UNITED EFFORT. Overheating caused all three of the SIGINT packages to fail on their first missions. After modifications in the United States they were returned to Vietnam. The UMA involved was called the Model 147E, a variant of the Ryan Firebee target drone that eventually became known as the Lightning Bug. It was also equipped with an active radar-enhancing device to ensure the Fan Song radar would detect the platform. On 13 February 1966 a Model 147E variant of the Firebee made history when it detected the command link signal from the Fan Song E radar system used to control the SA-2 before it was destroyed. Arguably this was a pivotal moment in the Vietnam War.
Once the operation of the Fan Song E was understood, measures could be developed to reduce its operational effectiveness. There were several ways in which this might be achieved. For example, one approach would be to try to jam the radar system. That often required a significant amount of power and airborne platforms had their limitations in this respect. Another more subtle approach was to manipulate the operation of the radar itself or the command guidance link to the missile in flight. Each alternative had its challenges.
Having processed the intelligence information collected from that mission, the United States Air Force could set about deciding how to degrade the operation of the two uplink channels used to control the missile. The link itself was found to be unencrypted. The designers had presumably reckoned on not having to bother to encode the link as the chances of an enemy getting close enough to interfere with the command link seemed unlikely. That is not a view that SAM missile designers would take today.
On the Fan Song E command link United States intelligence analysts found four quite distinct commands were transmitted to the missile in flight. These were the K1 and K2 waveforms which commanded the missile to climb/dive or turn right/left. The K3 waveform armed the proximity fuse and the K4 programmed the proximity-fuse delay on the warhead depending upon the engagement geometry. In operation the Fan Song E radar tracked the target and the transponder beacon on the SA-2 and continuously developed an optimal trajectory for an intercept.
Two control laws were also at the heart of the algorithm calculating the flight path. The Treokh Tochek or ‘three point’ control law was based on calculating the line of sight from the radar to the target. This had an important weakness that enabled the missile to be defeated by conducting high-G manoeuvres. But for slow transport aircraft this algorithm would provide a deadly solution. The alternative was called the Polavinoye Spravleniye (half correction) technique. This was more sophisticated and was to be used against highly manoeuvrable targets such as fighter jets. The selection of which algorithm to use had a huge impact upon the effectiveness of the SA-2. Warsaw Pact operators and their Vietnamese colleagues proved the more adept at using the missile than other users in the Middle East.
Commentators have suggested that this single mission provided the justification for the development of the entire Model 147 programme. It led to the development of a radar warning receiver called the AN/APR-26 that was to be fitted to United States aircraft operating over Vietnam. It warned the pilot when the command signal became active, indicating that a launch of an SA-2 was imminent. Another development was based on the idea of jamming the Fan Song radar to deceive it. Signals from the Fan Song would be received, slightly delayed and then re-broadcast to the receiver. This fooled the radar system into believing the target was in a different location. This equipment was known as the AN/ALQ-51 Shoe Horn jamming system and it operated in E-Band. The equipment was also carried on the EA-6A Intruder aircraft. In service, however, doubts were to emerge as to the precise effectiveness of the Shoe Horn equipment.
Alongside this specialist mission the United States Air Force was still conducting low-level flights with the Model 147J variant of the Firebee. Its attrition rate was high, so in order to sustain the operational tempo some of the Model 147G platforms were converted to the Model 147J configuration. The Model 147H was used to complement the low-level operations of the Model 147J. It had a more powerful J69-T-41A engine fitted that gave it the ability to fly up to altitudes of 19,800 metres (65,000 feet). While this was on the edge of the SA-2 MEZ (Missile Engagement Zone), it was thought the stealthy characteristics of the UMA would reduce the range over which the Fan Song radar could acquire and track the platform. Time would show that was not the case.
At the time stealth technologies were in their infancy. A special coating of paint applied to the jet intake provided some reduction in the radar cross-section but that was insufficient to reduce the threat. To help improve the survivability of the platform an RWR (Radar Warning Receiver) was added to the payload. This would provide a warning when it was being illuminated by an enemy radar system. A pre-programmed 30˚ turn would then occur in an attempt to throw off any engagement by an enemy missile. With missile systems agility improving all the time, this was not a fight a UMA could win.
What was needed was a more radical approach. Another box was added to the payload of the Model 147H. This was a jamming system called River Bouncer. It provided a signal that tried to disrupt the operation of the Fan Song radar. These measures did have a positive effect on the survivability of the UMA.
A subsequent refinement of the platform resulted in the development of the Model 147T which could fly up to 23,000 metres (75,000 feet). This entered service in April 1969. The Model 147H was phased out of operations in September 1972. A few months earlier high-altitude flights by the Model 147T over North Vietnam were stopped. The risks to the platform were simply too high. However, as a result of the loss of the EC-121 and all its crew in April 1969 along the border with North Korea, a new variant of the Model 147T appeared. This was the Model 147TE, known as Combat Dawn.
This UMA was the first of its type. The payload was dedicated to the SIGINT mission. It was able to operate at altitudes up to 21,336 metres (70,000 feet). This gave it improved slant range to look deep into a target country to collect SIGINT information. Intelligence material that was collected was downloaded in real time to the controlling ground station. This provided the basis for similar line-of-sight downloading of raw intelligence material on a range of other platforms. Control over the platform could either be accomplished from a ground station or the DC-130 launch aircraft. Recovery of the platform was by helicopter snare.
Initial tests of the Combat Dawn system involved it being launched from a DC-130 aircraft. Once declared operational, Combat Dawn flew twenty-two missions over North Korea and accumulated 61.5 hours in the air. Its attrition rate saw one Combat Dawn lost every ten and a half missions. With the addition of external fuel tanks the UMA was able to increase its mission duration to up to eight hours. Plans were put in place for the development of a twelve-hour mission on a variant of the platform known as the 147TL. Combat Dawn became the primary SIGINT sensor platform used by the United States, flying over 500 missions between its introduction into service in 1970 through to 1975.
It was also around this time that the United States Air Force and the Royal Air Force accepted that high-flying manned bomber missions over the Soviet Union using their strategic bomber force were no longer feasible. If the Royal Air Force’s V-Force was going anywhere near the Soviet air defence systems it was going to have to do it at very low level, around 80 metres (250 feet).
These developments of the Model 147H and the Model 147T raise an interesting issue over the cost benefit equation being applied to UMA at this point. As target drones, the issue for designers was all about simplicity. After all, if a missile fired at the target drone was armed there was a possibility that it might actually destroy it. The view had to be that target drones were ultimately disposable objects. However, as the first major revolution in UMA capabilities occurred, what became valuable was the intelligence information that it had collected on its mission. Therefore the priority was to recover the UMA and re-use it on another mission.
Survivability now became the order of the day. If that meant additional electronic equipment such as RWR and jamming systems had to be deployed as part of the payload, then that was accepted as long as the chances the UMA would return back to base were improved. With Soviet radar and technical developments, the high-altitude reconnaissance mission in what was an increasingly hostile (non-permissive) environment that cost-benefit equation meant that new payloads would have to be introduced on the platform. From a survivability viewpoint high-altitude missions were simply no longer viable. Until imagery could be delivered digitally in real time via satellite communication links, other means of intelligence collection had to be found.
Current UMA, such as the Predator and Reaper, operate in permissive environments. Periodic claims by senior Taliban spokespeople claiming that UMA have been shot down are often opportunistic statements allied to crashes caused by operational defects. This may not be the case in the future if a state-on-state war were to break out. The issues over survivability would then re-surface.
In the latter days of America’s involvement in Vietnam the Model 147 was to see some final iteration in its design. The Model 147S was a variant whose wing structure was changed to overcome a number of limitations associated with the Model 147B. At low level they did not generate enough lift. They also did not give the platform sufficient manoeuvrability. The wing span was reduced to the original 4 metres flown on the first generation of Firebees.
The Model 147S was also equipped with a new camera system that replaced the dual-configuration camera carried in the Model 147J. The new camera was able to obtain 30cm resolution along a strip 96 kilometres (60 miles) in length. On good days that resolution could even be halved. The new platform went into service as the Model 147SA in December 1967. It was, however, going to suffer a high rate of attrition as it tried to image targets over the heavily-defended areas of Hanoi and Haiphong. Its operating altitude, and hence the viewing geometry of the sensor system, was adjusted in order to let the platform fly at 150 metres (500 feet) instead of the initial configuration three times higher.
The backbone of the UMA sorties over Vietnam was to be the next iteration of the Firebee. This was the Model 147SC. It flew around half the total missions that eventually took place over Vietnam. This was the variant of the Model 147 that was produced in the greatest numbers. It incorporated an improved Doppler navigation system and digital flight controls that helped to improve flight accuracy. It was known as the Buffalo Hunter by its air force crews and went into service in January 1969.
The Model 147SRE was a variant of the Firebee that was dedicated to nighttime reconnaissance. It was equipped with an infrared strobe that provided illumination of the ground beneath the platform. Its imagery was recorded on infrared film. The material collected, however, proved to be difficult to interpret. A Model 147SC/TV also was developed to provide real-time television imagery that was relayed to the DC-130 launch aircraft. However, image quality at the time was low. Improvements were also made to the navigation system with the Model 147SDL including a Loran receiving system. This was an American development of the Gee radio navigation system pioneered by the Royal Air Force in the Second World War for bombing raids over Germany.
Naval variants were also developed that used a RATO booster. These were designated the Model 147SK and entered service in 1969. After take-off the UMA would initially be flown by an operator located in a Grumman E-2A Hawkeye AEW aircraft operating from one of the United States aircraft carriers operating in the area. They flew the UMA to a designated check-point where the control was handed off to the internal flight systems. Recovery was made by helicopter. In total several dozen flights were made by the United States navy under the operational name of Belfry Express. The reasons behind the use of this remain unclear. The last sortie was flown in May 1970 after it had only been in use for barely a year. It had been a tentative initial start for the navy in UMA operations.
In 1968 a total of 340 missions was flown by Model 147 variants. This was over three times the sortie rate achieved in the previous year and more than the total flight operations achieved over Vietnam up until that point. This was a major point in the war when the North Vietnamese launched the Tet (year of the monkey) Offensive on 30 January. This saw coordinated attacks launched across South Vietnam in an audacious bid to win the war. Thirty-six of forty-four provincial capitals were attacked. Fighting was particularly heavy around the United States combat base at Khe Sanh. While it is difficult to establish precisely where the Model 147 UMA were flown during the year, it seems more than coincidental that the sortie rate in 1968 occurred at the time of the Tet Offensive.
In subsequent years the sortie rate for the Firebee increased in 1969 to 437 before levelling off for the next two years. In 1972 at the time of the Operation LINEBACKER bombing raids against strategic targets in North Vietnam the highest recorded rate of sorties occurred at 570. By 1973 this had reduced again down to 444.
Other improvements also occurred in flight control systems technology, such as the gyro systems. The Model 147SB also included the capability to climb and descend the platform between pre-set altitudes to introduce a more random element into its flight path. Slowly but surely, developments in sensor and flight control technologies at this time were laying the baseline for future generations of UMA. In the crucible of war the UMA had taken its first steps from being a target drone used in peacetime to validate the performance of missile systems to being an active capability in a hostile environment.
Over the duration of the American involvement in Vietnam 1,016 Lightning Bugs were to fly a total of 3,435 missions. In the course of flight operations 578 were lost either to enemy action or as a result of an accident. The vast majority of the total missions flown were reconnaissance missions. It became the workhorse of operations in environments that were considered to be becoming increasingly dangerous. In total twenty-three variants of the Lightning Bugs were used in the intervention in Vietnam. One-seventh of them were shot down by ground defences. Some of the UMA attained almost heroic status as they caused Vietnamese pilots to crash while trying to shoot them down. One Lightning Bug was even awarded the status of ‘ace’ for being involved in five Vietnamese fighters being downed. One flew sixty-eight missions before it too was shot down on 25 September 1974.
The end of the military involvement was not to herald the end of the Firebee. While being at war had created the dynamic for quite specific developments in UMA technologies, as America re-trenched into its post-Vietnam introspection the main focus shifted back towards the Cold War and operations in Europe. Over Vietnam a variant of the Firebee (Model 147NC) had been fitted with chaff dispensers as well as active jamming systems. These were to fly escort missions alongside manned bombers and lay down a carpet of chaff that would disrupt the operations of enemy radar systems.
In Iraq in 2003 Firebees flew their last combat missions performing this role. In total five Firebee platforms were involved in the opening salvos of the Second Gulf War. Only one DC-130 remained equipped to control the Firebee and it was unserviceable on the opening night of the air campaign. Two were therefore launched by RATO. On the second night three were launched from the DC-130. There was no attempt to bring back the Firebees for another mission. They were sent on their way until they ran out of fuel. The wreckage of the platforms was shown on Iraqi television with an accompanying narrative that suggested manned aircraft had been shot down.
After the Vietnam War the SEAD mission was downplayed in new developments of UMA. Image intelligence became the mission priority for UMA in the west and in the Soviet Union and China. The SIGINT mission was not a priority for UMA as far as many states were concerned. That mission would be carried out by manned aircraft, a viewpoint that still applies today. The SEAD role for UMA seemed destined to have been a brief one.