F-111 in Vietnam | COMBAT LANCER

In the late 1960s, the F-111A first saw action in the Vietnam War, marking the beginning of a legendary career. Yet, while it would go on to become an icon, these early years have since been largely overlooked. Today, the F-111A is often remembered as a dangerous early build of the aircraft, and its service in Vietnam as a limited test of the platform, which included some accidents. The story often ends there.

In fact, over its two deployments, the F-111 became one of the USAF’s best performers, alongside the A-7D.

These two deployments – in 1968 and 72 – were not only crucial for the further development of the F-111 itself, but were also a test of newer, more advanced capabilities that opened up new strike options for the US Air Force.

This first fateful deployment – Combat Lancer – was costly. On paper, the F-111 seemingly failed in combat. But, upon closer analysis, its role, capabilities, and the limited sorties it flew during Combat Lancer paint a more nuanced story; one in which a few unfortunate malfunctions overshadowed what was a highly impressive demonstration.

F-111 ARRIVAL

The F-111’s arrival in the mid-60s brought with it an array of new capabilities to the US Air Force. In two primary variants – the F-111A and FB-111A – the platform would be flexible in both tactical and strategic bombing roles.  A suite of cutting-edge hybrid digital systems would make it one of the most precise strike aircraft ever produced, complete with good range and payload.

The idea of validating the jet in combat was soon put forward; Since its first flight in 1964, Robert McNamara had pushed the F-111 – or TFX – relentlessly for real-world testing, under the project name ‘ICARUS’. The obvious theatre of operation was Southeast Asia.

OTHER CHALLENGES

The challenges the F-111 would have to face in Vietnam were many. Since April 1965, radar-assisted air defences had saturated the airspace in the North. Beyond actual SAMSurface-to-Air Missile: A ground-based or ship-launched guided missile system designed to detect, track, and destroy enemy aircraft, helicopters, crui... More emplacements like the Fan Song, other powerful monitoring systems provided wide coverage. Among them were the P-35 Bar Lock and P-20 Moon Face warning radars.

Tactical Air Command had other problems as well. Paveway I wasn’t yet operational, so laser-guided precision weaponry was still largely out of reach. As we’ve discussed in the past, introducing laser- or electro-optical-guided weapons not only improved accuracy against bridges and the like, but also freed up the aircraft themselves.

Up until this point, general-purpose dumb bombs had been the go-to for strike missions. Given the wide circular error probable on most aircraft, this meant carrying large payloads; the idea was to ripple the stick across a target area and hope for a hit. In the south, the Hun would fly most of these missions, with limited risk. Up north, however, the job fell to the F-105. These bogged-down Thud flights were infamously vulnerable to SAMs and aircraft intercepts, meaning Phantoms had to be sent up as well for MIGCAP coverage.

The few Air Force aircraft that could strike fast and with better accuracy were only just arriving – the F-4D with WRCS was particularly accurate. Still, it wouldn’t be ready in serious numbers until late 1968.

Since the war had flared up in 1964, a consistent problem had been the ability to hit targets day or night, and in poor monsoon conditions. Several iterative programs tried to address this, but most relied on overly complex ground networks. From July 1966, the Air Force used an elaborate guidance network called Combat Skyspot to enable all-weather, day-and-night precision bombing. Using Hun crews as pathfinders for larger Thud flights, Combat Skyspot would guide crews to an IP, then lock them with a radar computer called Miscue 77, which would automatically compute ballistics and bomb impact points. The crew would then be cued when to release, and relay this to the others in the flight.

This had been a good workaround, as it allowed old workhorses like the Hun to strike reasonably well even at night. As a side note, it was one of these systems housed at Lima Site 85.

By 1968, special F-4Ds had arrived with LORAN compatibility, an even more accurate system, not reliant on a ground controller cueing the crew. The jets, with distinct ‘towel racks’, would lead in larger phantom flights and cue their release point.

However, when it came to high-precision blind bombing systems not reliant on external tech, the solutions were initially few. The B-52 had an offset bombing mode called OAP, but it was an obvious target when it flew high and slow.

One of the few exceptions had been DIANE, the digitally integrated attack suite on the A-6 Intruder. It allowed crews to fly low-level attack runs in any visibility. Groundbreaking for its time, this system had been the central focus during the Intruder’s development, and with good reason; solid-state electronics had allowed far more precise navigation and targeting equipment to be fitted.

The F-111 offered a similar, albeit still unrefined solution on paper. Just like the A-6, it would theoretically bypass all external contingencies – like tankers, LORAN, MIGCAP escort, and the like – giving crews a self-contained strike platform, complete with low-drift navigation, advanced ground mapping, and low-level capabilities. Where it lacked in systems refinement, as in the A-6, it would make up for it with an even more daring low-level terrain-following program and unmatched top speed. At night, 500 feet off the ground at 500 knots, it would be able to sneak in with minimal to no radar presence, strike on a single pass without having to see the target, and then escape.

F-111 ONBOARD TECH

The actual tech inside the F-111A that made this possible was extensive. Broadly referred to as the Mark I avionics suite, it would include several hybrid digital systems:

•         At the core of the suite was the APQ-113 multimode radar: used for ground mapping, ranging assistance, and limited air-to-air defence, it was both powerful and accurate, integrated into a central computing unit which received data from other sensors onboard to aid in navigation and target acquisition.
•         The AJQ-20 INSINS (Inertial Navigation System): A self-contained navigation system used in military aircraft that calculates position, velocity, and orientation wit... More, or more specifically BNS – for bombing and navigation system – would make up the core of the nav and weapons delivery suite
•         Based around gyros and accelerometers, it was nonetheless advanced, integrating hybrid digital components. Two modes were available: one for short trips, which worked on a flat plane reference, and one for long trips, which worked off a trigonometric spherical reference.
•        It also worked out equations for weapon ballistics. This could be chosen in several modes, ranging from an early CCIP mode using the basic pipper, to an early CCRP mode, referred to as Auto Bomb. Auto Bomb used a cue displayed over the radar’s ground-map image. The pilot could slew this cue across the map to the desired target point. As he moved it, the AJQ-20 continually calculated the corresponding ground position, including the target’s elevation. It determined the precise point in the aircraft’s flight path at which the weapon should be released. Once the pilot stopped slewing and selected the desired point, the system could then provide the release cue needed to deliver the weapon onto that point.
•         Another rather elaborate mode was Offset Aimpoint. This pre-planned function let the crew select a prominent, easily identifiable reference point near the actual target. They then entered the target’s offset from that reference—in range, direction and elevation—into the computer. On the mission, the pilot only had to slew the cursor onto the reference point. The computer then applied the stored offset and generated the navigation and weapon-aiming solution for the actual target.

Beyond this, the system also assisted with more familiar attack modes such as dive and loft bombing. Loft attacks made use of the INSINS (Inertial Navigation System): A self-contained navigation system used in military aircraft that calculates position, velocity, and orientation wit... More solution, while dive attacks relied primarily on radar ranging, much as they did with the Phantom’s WRCS system.

•         The ALR-62 RWR would act as the main electronic support measure. A digital system, it was among the earliest RWR compasses to show actual boxed threat symbols rather than strobe lines. It would receive information from a variety of sensor types, not just one set; they included standard crystal video, alongside superheterodyne and YIG receivers.
•         Other smaller defensive systems would work in conjunction with it: chaff and flare, an active jammer – the ALQ-94 – and even an early, passive infrared warning receiver: the AAR-34, a cryogenically cooled infrared sensor on the vertical stabiliser. Paired with a countermeasures system, this would counter a more pronounced low-altitude threat: heat-seeking missiles.
•         The terrain following system would be handled by the APQ-110 radar, a dual-redundant system, offering the pilot the ability to fine-tune cruise altitude and select the smoothness of the ride.
•         Lastly, the ASG-23 optical gunsight would visualise data to do with bombing, target acquisition, and navigation. Before the Buccaneer and A-7D bought into the digital HUDHUD (Head-Up Display): A transparent display system that presents critical information directly in a user's line of sight, eliminating the need to loo... More, this was among the best projected sights any aircraft manufacturer had built.

With all systems linked, the aircraft allowed hands-off, high-speed flight as low as 200 feet off the deck, in any weather, night or day.

While this early model lacked the more advanced tech we’ve discussed in other videos – like the 150mm filmstrip projected map display – the Mark I suite was still more capable than most else the Air Force had.

PREPARATION

The first sets of F-111s off the production line would be part of a real-world evaluation scheme to validate the new platform. This was – obviously – not standard practice, but with waning Navy interest in the platform, justifying its continued production for the Air Force was likely a priority for Washington.

The first 18 airframes would be sent to two designated test sites: Eglin and Edwards Air Force Base, under the program designation Combat Bullseye I. This evaluation scheme – begun in early 1967 – was to be a systems performance validation of the attack and terrain-following radar sets.

Shortcomings were noted, but the core systems were deemed functional for real-world operations.

By this point, the idea of real-world combat testing was now within reach. The plan was to rush a detachment to Thailand with the type and run a limited-scope, high-intensity evaluation at night and possibly in poor weather, then use the findings to refine the F-111 further.

Detachment 1 of the 428^th Tactical Fighter Squadron was selected to run the operation, both validating the systems and then testing them on the battlefield.

With good signs for a deployment in the coming year, two pre-combat programs began. The first – in June 1967 – would be a further systems validation check, and a slight modification program, designated Harvest Reaper. The Reaper mods would include a refined threat detection and countermeasures suite, and a retuned ballistics unit for the onboard computer suite. Finally, it would be painted in the typical Southeast Asia scheme, with a few changes: rather than a white tail code and anti-flash white underside, the features would be done in black, evidently due to its expected night tasking.

The second program was Combat Trident. This was to be the actual crew training module before deployment. In early 1968, crews were selected and then sent to Nellis. 22 crewmen arrived. Before them were some of the 31 initial airframes off the Fort Worth assembly line, in pre-production spec. One of the pilots—Colonel Ivan Dethman—had actually flown up the newest airframe the previous October as part of one of the many elaborate public demos; it had been flown all the way to Nellis from Fort Worth using terrain-following radar, never ascending above 500 feet.

The training that followed proved somewhat eventful. Captain Joe Hodges would later recall that the types they were given had pre-production components and were awful. He had spent 500 hours in the Phantom and never saw a compressor stall. During his first flight sitting in the right seat, his pilot pushed the throttle up for take-off when both engines stalled. They ran the procedure again, and both engines stalled again. Finally, they managed to take off and fly up-range toward the bomb range at Nellis, when Hodges recalls hearing a loud bang. The screens fogged up. With no visibility, they turned around, headed back, and were forced to rudder into a crab to line up an approach for landing.

This first experience wasn’t reassuring; the TF30 engines were already proving touchy, and the report said the bang came from a hailstone – apparently from a storm the crew never saw.

As Major Sandy Marquardt recalled, during training the crews got a lot of unusual attention; reporters were always trying to get information for stories, and Air Force brass followed them around, wanting to know if the plane was living up to General Dynamics marketing claims.

The training profile also gained them a lot of attention; every night, they were consistently flying tests of the 200-foot mode on the TFR – the lowest mode it could be set to – and validating that it would indeed work without crashing into the ground.

The training program included particularly impressive mission profiles. Marquardt recalls setting up a simulated target in California or Florida. All the radar sites in the huge designated zone would then try to find the jet. The crew would then sneak in at low level, using terrain masking to develop their own ingress paths. As the crew put it, usually the first sign anyone knew they were in the area was from the roar of their engines

On March 6th, Trident would wrap up. The program had proved the aircraft had considerable potential —it could strike before anyone on the ground or at a radar site ever knew it was coming. It was the ultimate validation of the late 50s idea of low and fast. By this point, the F-111 faced intense media criticism and had yet to receive IOC. Nonetheless, the pilots were told they would head to Takhli Air Base in Thailand.

Under the designation of Combat Lancer, the crew ferried off with their six aircraft on the 15th. Upon arrival on the 17th, despite criticism shown in the media, the F-111 generated a buzz at base. An aircraft was bought out of the hangar and parked for display —a clear indicator that, despite the controversy, it was eye-catching.

On March 25^th, the aircraft would see its combat debut: a night sortie flown by Colonel Ivan Dethman and Captain Rick Matteis. The briefed target was a storage facility on Hon Co Island, with an egress out over the Gulf of Tonkin. Taking off, the crew flew in at 500 knots, 500 feet, releasing a stick of 12 M-117s across the target area, before heading over the ocean. The strike mission was a complete success; without ever seeing the target, the coordinates were overflown and struck, with no immediate danger to the aircraft.

Now validated in combat, sorties flew every night with similar effect. However, disaster would soon strike.

On March 27^th, the third night after debut, airframe 66-0019 took off, but was soon forced to turn around and land after experiencing hydraulic issues. This was the first ground abort of the operation. Later that night, a second jet took off – airframe 66-0022, callsign Omaha 77, flown by Major Henry McCann and Captain Dennis Graham. Flying up through Thailand to hit a northern target, the crew suddenly dropped off scope, and communications were lost.

The North Vietnamese claimed they had shot it down somewhere in Route Package III or IV; however, the Air Force doubts the claim, believing it never even left Thailand. Somewhere on the ingress route, the aircraft likely crashed, never to be found. The crew were declared KIA.

While missions continued, this loss hit the small crew hard. Unfortunately, it would not be the last. Two nights later, another incident would occur. Major Sandy Marquardt and Captain Joe Hodges took off and flew into Laos on an ingress route, callsign HotRod 76. As they neared northern airspace, they decided to descend from 10,000 feet. Suddenly, the aircraft pitched up uncontrollably, and then began to roll. The crew ejected in the escape capsule and survived. Upon finding the wreckage, it was found that the accident had been caused by a catastrophic failure of an actuator value, causing the stabiliser to snap to maximum deflection.

The four remaining aircraft were temporarily grounded, and replacements headed over on April 5^th.  On April 22^nd, a third and final crash would occur. Flying airframe 66-0024, Lt Col Edward Palmgren, along with a Navy exchange pilot, Commander David Cooley, took off en route to a target on the Ho Chi Minh Trail, callsign Tailbone 78. Radar had been tracking them for a while before the crew decided to drop to 500 feet. They were never heard from again. Listed as KIA, the US were once again unable to find the wreckage, and intelligence indicated that the enemy hadn’t either. This mysterious crash was listed as another actuator failure, at such an altitude that the crew had no chance.

With half the original fleet gone following the third crash, the program was put on hold. With a 50% loss rate for the initial fleet, and four crewmen gone, Combat Lancer was deemed an overly costly endeavour. The final outcome of the one-month operation was interesting; despite this high loss rate due to the same mechanical faults, the north hadn’t been able to hit it; over 55 night sorties flown, most had hit their target without issue. This proved the core system functionality and logic worked.

By November 22nd, Combat Lancer crews had ferried back home to Nellis, and the F-111’s presence in Vietnam was brought back to zero.

CONCLUSION

The program ended just in time. Not long after their return, the F-111’s wing passthrough box issue was discovered during fatigue testing. Further tests over the following months revalidated this weakness, and then in early 1969, the first crew was lost in a crash at Nellis, caused by the complete detachment of the wing. In February 1970, the costly but necessary decision was made to continue the program, but ground the entire F-111 fleet; every airframe made before the crash would be tested under an extreme -40 degrees Fahrenheit, 7G cold-proof load test before they would be given back.

The TFX period in the 1960s was certainly strange and controversial. On the one hand, McNamara’s insistence on the program made it costly and time-consuming. On the other hand, despite the Navy dropping out, he had essentially brute-forced the creation of the most technologically advanced strike platform in the world.

As recalled by the crews after Combat Lancer, the tool they had on hand was something that no one else possessed– in need only of refinement. It was fast, with good range, good onboard tech, and great precision. In the dark, no one could touch it, and if planned correctly, no one would even know it was coming; a serious standoff warning for a potential enemy the US Air Force might face. Despite being temporarily grounded due to safety concerns, the F-111 and FB-111 would soon give both Tactical and Strategic Air CommandThe U.S. Air Force’s primary organization for long-range nuclear deterrence during the Cold War, responsible for maintaining and, if necessary, delive... More an unmatched precision-strike platform.

By early 1969, the F-111 development team had a long but clear path ahead; they needed to improve reliability. But thanks to Combat Lancer, the designers now had confidence in their product; the aircraft could do exactly what they intended— and it wouldn’t be long before it returned to Vietnam to prove itself.