AIR & SPACE MAGAZINE

Where have all the phantoms gone.

How a fighter-bomber-recon-attack superstar ended up as fodder for target practice

Ralph Wetterhahn

DJ09_Phantom Flash.jpg

The F-4 Phantom II lives. But the life it leads today is an odd one.

It still flies in other countries; in northern Iraq, for example, the Turks use it in combat with the Kurds. But in the United States, it leads a twilight existence. It’s a warplane, but it no longer fights. Its mission is weapons testing, but no pilot flies it. Mostly, you’ll find these F-4s either sitting in the desert or lying at the bottom of the sea.

The F-4 entered service in 1960, flying for the U.S. Navy. After studying its potential for close air support, interdiction, and counter-air operations, the Air Force added the F-4 to its fleet in 1963. Eventually the Phantom ended up even in the U.S. Marine Corps’ inventory. In four decades of active service to the United States, the aircraft set 16 world performance records. It downed more adversaries (280 claimed victories) than any other U.S. fighter in the Vietnam War. Two decades later, it flew combat missions in Desert Storm.

In 1996 the aircraft was retired from the U.S. fleet. But the venerable McDonnell design has one last mission to perform for the military: to go down in flames.

Since 1991,  254 Phantoms have served as unpiloted flying targets for missile and gun tests conducted near Tyndall Air Force Base in Florida and Holloman Air Force Base in New Mexico. The use of F-4 drones (designated QF-4s) is expected to continue until 2014.

When an airframe is needed for target duty, one is pulled from storage at Davis-Monthan Air Force Base in the Arizona desert. The airframe is given refurbished engines and instruments, then sent to Mojave Airport in California. There, BAE Systems turns the aircraft into remote-controlled drones, installing radio antennas and modifying the flight controls, throttles, landing gear, and flaps.

QF-4 production test pilot Bob Kay is responsible for testing the converted aircraft, then flying them from Mojave to Tyndall and Holloman. Kay has been captivated by the F-4 since the age of seven, when his father took him to an airshow. “I saw a Navy A-3 refueling two Phantoms as they flew over so low and with that noise,” he says. “That’s all I remember of that airshow, but I knew I wanted to fly that fighter.”

I ask if he has any second thoughts about being part of a system that destroys an airplane he loves, an aviation legend.

He thinks for a moment, then says, “What better way is there for a warrior to end its life than to go down in a blaze of glory?”

The Phantom has been called  “double ugly,” “rhino,” “old smokey,” and monikers even less flattering. The design does have its share of ungainly bends and angles. The horizontal stabilizers droop 23.25 degrees. The outer wing sections tilt upward 12 degrees. When an engineer looks it over, the first thing that probably comes to mind is “stability and control problems.” A brutal example of that weakness occurred during a May 18, 1961 speed record attempt. While Navy test pilot Commander J.L. Felsman flew below 125 feet over a three-mile course, his F-4 experienced pitch damper failure. The resulting pilot-induced oscillation generated over 12 Gs. Both engines were ripped from the airframe and Felsman was killed. (A later attempt succeeded.)

Control sensitivity varies widely. It takes full aft stick to raise the nose for takeoff, yet at certain fuel loadings and at speeds just above Mach 0.9 at low altitude, moving the stick only one inch can produce 6 Gs on the airframe. At above Mach 2, on the other hand, the shock wave that is created moves the center of lift so far aft that pulling the stick all the way back produces only about 2 Gs.

With all its peculiarities and faults, legions have had love/hate relationships with the aircraft. “The F-4 is the last of the fighter pilot’s fighters,” says BAE’s Bob Kay. “You have to fly the F-4.” It has none of the bells and whistles of next-generation fighters. Instead of the multi-function flight displays found in modern fighters, the cockpit instruments are “steam gauges”—round dials with needles. It has an inertial navigation system, best described as cranky. There is no flight management system, no GPS, no Electronic Flight Instrument System (EFIS), and no “Bitching Betty” voice system to alert the pilot to hazards. You have to navigate, bomb, shoot missiles, fire the gun, look for problems, and evaluate every one of those actions instrument by instrument. For the pilot, this means a lot of time is spent head down, analyzing instrument data; in modern aircraft, on the other hand, much of the information is presented compactly, in head-up displays above the instrument panel.

My affair with the Phantom began upon graduation from pilot training in 1964, when I landed a tour in the Air Force F-4C. Though the Navy and Marine Corps assigned radar operators to the “pit,” as we referred to the second seat, the Air Force thought it would be more effective to use the configuration for two pilots. Wrong. No true fighter pilot chooses to serve as

copilot. The assignment was akin to a shotgun marriage. For two years I languished six feet behind my more experienced comrades, calling off altimeter readings as they bombed, strafed, and fired rockets in training exercises on the gunnery range. Backseaters had to beg, cajole, and whine for stick time, and when we got it, we found that every aspect of flying the F-4 from the rear cockpit was a nightmare. The meager instruments were placed haphazardly in a straight line across the panel. The useless clock and G-meter were located in the center. Why? Because they fit there! Instrument approaches gave you a migraine. And to spot the runway, you had to peer through a knothole on either side of the cockpit, which made landing from the pit an adventure, especially with a crosswind.

Front-seaters were not always thrilled with the F-4 either. In 1972, during his second tour in Vietnam, U.S. Air Force Major Dan Cherry, now a retired brigadier general, flew 185 combat missions in the Phantom; today he recalls: “The F-4 cockpit was uncomfortable, the instruments were poorly arranged, crew coordination was a hassle, it was ugly, and it used fuel like nobody’s business.”

Crews that flew the airplane for the Navy had their own share of problems. By 1966 the Rolling Thunder bombing campaign waged by the Navy and Air Force had really heated up. Large formations of fighter-bombers were striking targets in the Hanoi area daily. That year Commander Dick Adams’ squadron flew combat in F-4s off the carrier USS Franklin D. Roosevelt. Each Phantom launched from the Rosie’s short catapult with four 500-pound and four 1,000-pound bombs, plus an empty centerline tank, which was refueled during climbout. Before a carrier landing, Phantoms had to achieve a certain landing weight; landing heavy would overstress the arresting cables. For this carrier, the F-4 was a heavy aircraft, and as such could try an approach with fuel for only one or two attempts. On the 1966 cruise, one of the squadron jets on a landing attempt was waved off, and when the pilot ran out of fuel before completing a second pattern, the engines flamed out and the aircraft went deep-six. The crew survived.

In March 1966, I was told that if I agreed to take a combat tour, I’d get the front seat. Are you kidding?  I made my first front-seat flight at MacDill Air Force Base in Florida. I still remember it: a gunnery mission. And oh, the visibility from the front

chair! My landing was the smoothest of “grease jobs.” At that moment, the shotgun marriage turned into a love affair.

After passing my checkout flight, I was stationed at Ubon Air Base in Thailand, a member of the 555th—“Triple Nickle”—Squadron in Colonel Robin Olds’ famed Eighth Wing.

At Ubon, the F-4 was all things to all people. One squadron flew only at night, popping flares and dropping bombs. The other two squadrons flew both day and night, dive-bombing bridges, strafing ground targets, rocketing truck parks, and tangling with the ever-elusive MiGs over Hanoi.

On October 11, 1966, I discovered how tough the Phantom was. An 85-mm round blew a four-foot section off my right engine, and the aircraft caught fire. Still, it held together through the 400 miles back to Ubon.

By the end of 1966, the Phantom had revealed a host of shortcomings. Number one was the dismal record of missile hits against the North Vietnamese MiG-17s and MiG-21s. The AIM-7 radar-guided missile had a probability of kill below 10 percent. Richard Keyt, who flew F-4s for the 35th Tactical Fighter Squadron during the Vietnam War, recalls: “Our missiles were designed to work in a non-maneuvering environment—a non-turning, 1-G shot at the bomber target flying straight and level at high altitude.” The reality: “F-4s fired in high-G turns at small MiGs that were turning hard and pulling Gs.” To remedy the problem, the Air Force expanded its Weapons System Evaluation Program (WSEP) at Clark Air Base in the Philippines. Combat crews were given practice in firing missiles at towed radar-reflective targets.

My backseater, First Lieutenant Jerry K. Sharp, and I took part in that exercise over the South China Sea in December 1966, scoring a hit. On January 2, 1967, we used the skills we had honed in that exercise when we merged with a flight of four MiG-21s that were turning hard to get at us. Sharp got a radar lock-on while under heavy Gs. Then I centered the steering dot, fired two AIM-7s, and watched as the second missile exploded and tore the tail section from the MiG in front of us.

For other F-4 shortcomings, the military contracted out quick fixes. Modifications included the installation of Radar Homing and Warning (RHAW) gear—a cockpit system that alerted pilots when their aircraft was being tracked by anti-aircraft-artillery radars or surface-to-air-missile sites. Also added were radar jamming pods, plus chaff and flare dispensers used in combination to confuse tracking radars and to dupe radar-guided or heat-seeking missiles.

The C variant had a number of design problems; one of the biggest was lack of a gun. The rules of engagement over Vietnam required that an adversary be identified visually before a missile could be fired at it. The MiGs were small, and to make the ID, shooters had to get close, often much less than the minimum distance that the AIM-7 radar-guided and AIM-9B heat-seeking missiles required to hit a target. At short range, “if you didn’t have a gun, you couldn’t shoot down anything,” says Rich­ard Keyt. The quick fix was the SUU-16/A gun pod with the M61A1 20-mm cannon.

But without a lead-computing sight and with no tracer ammunition, F-4C pilots were denied the visual cues needed to correct aiming errors. Then, in 1967, the F-4D arrived. The D model introduced a lead-computing optical sight for use with the gun pod. In addition, the normal ammunition load now included tracers.

On November 6, 1967, the gunfighter Phantom proved its worth. Captain Darrell “D” Simmonds and First Lieutenant George H. McKinney Jr. were escorting a flight of F-105s that came under attack by two MiG-17s. “We picked up the MiG-17s visually that were shooting at the Thuds [F-105s],” says Simmonds. “I was able to get in there and maneuvered for a perfect ‘uphill dart’ shot. I hit him, came alongside, and looked at him, and he looked at me, then ejected just before the plane hit the trees.” McKinney spotted another MiG-17 and Simmonds swung into a hard turn, accelerating as he lined up for the shot. “We were close, but I didn’t want to miss the opportunity,” the pilot remembers. “I fired and he blew up.” Later, Simmonds realized: “We had used just 497 rounds for the two kills—less than five seconds of firing.”

The D model, however, was not a cure-all. “The guns on the D hung externally, on the centerline, and that created drag,” says Keyt. As for the missiles, the underperforming AIM-9B was abandoned for the Hughes AIM-4D Falcon. Designed to bring down strategic bombers, it required cooling of the seeker head prior to launch and needed a direct hit to score a kill. As pilots found out during what became known as the “Falcon Fiasco,” it came up short in a dogfight. Major James R. Chamberlain, a backseater stationed with the “Gunfighters”—the 366th Tactical Fighter Wing at Da Nang—notes, “The biggest problem with the AIM-4D was the limited amount of cooling time available [two minutes or less], which meant that the missile could not be pre-cooled for a quicker lock-on. And, once available liquid nitrogen was consumed, the missile was a blind, dead bullet—derisively called the ‘Hughes Arrow.’ ” After firing four of the missiles in combat without success, Robin Olds insisted the missiles cost him his fifth kill. He ordered them removed from his fleet.

The Air Force soon trashed the AIM-4D. Newer Sidewinders were substituted. The military also recognized the benefits of an internal gun: The F-4E, introduced in 1967,  had an M-61A cannon mounted beneath a solid-state AN/APQ-120 radar, both inside the aircraft nose. During the time Richard Keyt’s 35th Tactical Fighter Squadron was based at Korat air base in Thailand,  five squadron aircrews were credited with MiG kills, and four used the internal gun.

In 1973, during my third tour in Southeast Asia, I was assigned to the early E model. It was a dream to fly, not only because of the improvements made in gun and missile technology but also because the Air Force had realized the folly of putting two pilots in a fighter. After 1967, virtually all the GIBs—guys in back—were either navigators or radar intercept operators.

The follow-on Es brought enhancements: A horizontal tailplane with a fixed inverted slat gave improved control at high angles of attack. Leading-edge slats on the wings enabled tighter turns at slow maneuvering speeds. A Northrop system called TISEO (target identification system, electro-optical) identified airborne targets.

By the time my final tour was up, in 1974, a fleet of Phantom variants had safely taken me through a gauntlet of fire and flying experiences that would constitute the greatest adventures of my life.

Three-plus decades later, I was once again in the company of Phantoms. This time the setting was the tarmac at Tyndall.

The commander of the 82nd Aerial Target and Recovery Squadron, which conducts the drone shootdowns, is Lieutenant Colonel J.D. “Bare” Lee. A former F-16 pilot, Lee also has 1,500 hours in the Phantom. He still recalls the first time he took to the air in one. “I was shocked at how much more difficult it was to fly than I thought it would be,” he told me. “When I got home, I told my wife, ‘I think I just traded in a Porsche for a ’72 Cadillac.’ ”

At any one time, a total of up to 80 F-4s are stationed at Tyndall and at Lee’s Holloman detachment in New Mexico. Twenty-one Phantoms sat on a ramp called the Swamp, awaiting movement to Death Row, the holding area for the soon-to-be targets.

At mid-afternoon the drone mission briefing took place. The meeting included the drone “fliers,” Lockheed Martin personnel headed by pilot/controller Matt

LaCourse. “Today’s mission is in support of WSEP, so there’ll be a lot of shooters out there,” said Lee. “WSEP” is the same Weapons System Evaluation Program I had participated in four decades earlier in Vietnam, when I’d practiced shooting at towed targets from F-4s. Now the F-4 was the target.

LaCourse explained that four F-22 Raptors would each fire the latest AIM-120 air-to-air missile. The shooters and chase plane would take off from the main runway, while the drone used a strip three miles east.

Most Phantoms wind up in the Gulf of Mexico within one to three missions. But not all: One, nicknamed “Christine,” after the Stephen King book and film about a crazed car with a mind of its own, had survived 10 missions. Another, “Son of Christine,” has come back from 12 sorties, the current record.

Some drone missions are not meant to be shootdowns: The Phantom is loaded with missile jammers, and missiles without warheads are fired against the craft to test how well the jamming works. Other Phantoms are spruced up with Vietnam War-era camouflage and flown to airshows.

One Phantom was saved by its former pilot. On April 16, 1972, Dan Cherry, flying an F-4D, had scored a victory over a North Vietnamese Mig-21. Thirty-two years later, during a trip with friends to the National Museum of the Air Force in Dayton, Ohio, Cherry encountered the aircraft he had flown that day. It was on display in the little town of Enon, outside Dayton.

“In spite of her flat tires, weeds growing up all around, bird droppings everywhere, and faded gray paint, she was beautiful,” he recalls. “Walking around her and answering my friend’s questions made me realize how much I loved her and how much I owed her for taking such good care of me. Suddenly all those things that seemed like negatives before paled in comparison to the strong bond I felt at that moment.” Cherry took on the task of relocating the aircraft to the Aviation Heritage Park in Bowling Green, Kentucky, where it was restored and is now displayed. Then he decided to learn about the pilot of the MiG he had shot down. (Cherry’s story about meeting his former enemy in Vietnam will appear in a future issue of Air & Space/Smithsonian.)

At Tyndall, the heat and humidity hit my face like a wet washcloth. The van driver took us from Death Row to the end of the runway, where F-4E tail number 73-1165 was positioned about 20 feet to the right of the runway centerline.

I asked if I could approach the aircraft. My unit escort, Major Kevin Brackin, obtained permission. I got out of the van and walked across the concrete. When I reached the aircraft, I placed my hand on the radome. Because of the cloud cover, the nose was warm to the touch, not the usual egg-frying hot. The Phantom felt alive.

I felt a wave of dread. Within minutes this magnificent machine might be in pieces at the bottom of the Gulf of Mexico.

A photo was taken, and I headed back to the van to listen to the radio chatter.

Lee says it cost the Air Force $2.6 million to get the aircraft from the boneyard in Tucson to the runway at Tyndall. Is it worth it? “The F-4E has the built-in ability to launch flares and chaff and can carry an assortment of jamming pods, all of which put our latest weapon systems through their most rigorous tests,” says Lee. Had we taken the time to test our missiles properly in the early 1960s, the Vietnam air war might have turned out like the one over Baghdad: a clean sweep.

We positioned ourselves behind the drone to await the launch order. Both engines were started. The canopy was closed, and the self-destruct bomb was armed for use in case the drone went out of control. Finally, the intake screens in front of the engine inlets were removed.

Then came an ominous ground transmission: The “shooter aircraft have problems,” and a storm cell had slung cloud

layers over a wide swath of sky. We sat and waited.

Finally, after a 15-minute delay, the mission was ordered back on.

The drone launch order was soon passed, and the operators got the Phantom rolling. LaCourse made a correction to get the aircraft precisely on centerline as both afterburners lit. Fifteen seconds later, I watched the pilotless aircraft take off.

The F-4 proceeded out over the gulf. The first aircraft fired its missile. The ground controller monitoring the telemetry radioed the air crews: “No hit.”

The Phantom flew on.

My emotions tangled: I wanted the aircraft to survive, but I also wanted it to fulfill its intended mission.

The four F-22 Raptors spread out. Each launched a missile. Over the radio we heard “Fox-four”—all shooters had fired.

Then: “Splash.” A direct hit.

Brackin and I walked back to the van and got in. Brackin was staring straight ahead. Then he turned to me. “So now you know,” he said, grinning. “It takes four Raptors to kill an F-4.” 

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'Phantom of the Opera' takes a final Broadway bow after 13,981 performances

Jeff Lunden

Jeff Lunden

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John Riddle as Raoul, Laird Mackintosh as the Phantom and Emilie Kouatchou as Christine, take a bow at the end of the final performance of the Phantom of the Opera at the Majestic Theater in New York City on April 16, 2023. Timothy A. Clary/AFP via Getty Images hide caption

John Riddle as Raoul, Laird Mackintosh as the Phantom and Emilie Kouatchou as Christine, take a bow at the end of the final performance of the Phantom of the Opera at the Majestic Theater in New York City on April 16, 2023.

On Sunday night, April 16, the curtain will fall on the longest-running show in Broadway history. The Phantom of the Opera , Andrew Lloyd Webber's mega hit musical, is closing after more than 35 years.

The stats are absolutely staggering – since it opened on Broadway in January of 1988, Phantom has played almost 14,000 performances to audiences of over 20 million, grossing over $1.3 billion. An estimated 6,500 people have been employed by the production – including over 400 actors – and it takes a cast, orchestra and crew of 125 to put on the show. On Monday, it will all be over.

"I got the gig of a lifetime. There's no other way to describe it," says Richard Poole, who's been a member of the ensemble, playing small roles, for almost 25 years. "It's given me the ability to have security, to plan ahead," says Poole. "It gives me discipline and structure in my life, and it gives me a constant way to maintain my craft."

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Steve Barton (from left), Michael Crawford and Sarah Brightman during the curtain call at the end of the premiere performance of The Phantom of the Opera on Jan. 26, 1988 at New York's Majestic Theatre. Ed Bailey/AP hide caption

Musician Joyce Hammann has been at the show even longer than Poole: "I'm concertmaster at Phantom of the Opera , which is first violin. And holy moly, I've been there 33 and a half years." Hammann is one of several members of the orchestra to have a "Phantom baby" – her son, Jackson just turned 18. "This has been his home away from home," she says. "People [here] have watched him grow up. He had the pleasure of sitting backstage during Saturday matinees sometimes when I wasn't able to get a babysitter."

The Phantom of the Opera , for those who've never seen it, is the story of a disfigured genius who haunts the Paris Opera House, pining away for a young soprano, Christine, who's in love with a dashing count. People die, a chandelier crashes to the stage, but love kinda triumphs ... all set to a sweeping romantic score.

25 Years Strong, 'Phantom Of The Opera' Kills And Kills Again

25 Years Strong, 'Phantom Of The Opera' Kills And Kills Again

"I was very keen to write something which was a high romance at the time, having done Evita and having done Cats and various things, which ... didn't let me ... go in that direction at all," Lloyd Webber recalled in 2013, for the show's 25 th anniversary on Broadway. When he read Gaston Leroux's novel, he found the vehicle and collaborated with Richard Stilgoe and Charles Hart on the adaptation, directed by Hal Prince.

"I think the enduring appeal is because it's so romantic and because audiences escape into it," the late director said for the 25 th anniversary. "It has a world of its own. And whatever problems they have out on the street and in their daily lives, they come in here and it's like a little kid tripping on a fairy tale or something. Only this is a slightly dangerous one. But the point is, I think that they escape from reality for a couple of hours and in a romantic world."

Music Interviews

'phantom of the opera': 20 years in the pit.

"The Phantom being misunderstood, I think is a big symbol for a lot of people," says Ben Crawford, who now has the distinction of being the last Phantom to haunt the Majestic Theatre on Broadway. [Ed. Note: Laird Mackintosh played the Phantom at the final performance on Sunday, April 16, filling in for Crawford who was ill.] Like other Phantoms before him, he has a special relationship with the Phans who've visited the show over and over. Some even send him their own artwork. "They saw that I had dinosaurs in my room," he says, "because when I play with my kids on FaceTime, my son loves dinosaurs, so they 3D printed this velociraptor that's, like, in a tuxedo with a phantom mask. And it came to my dressing room in a box with, like, holes in it so it could breathe."

But even the longest running show in Broadway history has to close at some point. Producer Cameron Mackintosh says Phantom was losing money, even before the pandemic. So, last September, he and Andrew Lloyd Webber announced a final date. "The following week, we were profitable for the first time," Mackintosh said in a phone interview from London. "So, you know, it was the right decision to take at the right time. And, you know, I think people's memory now is back with people saying Phantom of the Opera is one of the great successes of all time, which is what one always prays when a great show finishes."

Not My Job: We Quiz T-Pain On 'The Phantom Of The Opera'

Wait Wait...Don't Tell Me!

Not my job: we quiz t-pain on 'the phantom of the opera'.

So, Phantom is going out with a bang – it's been selling out again. Music supervisor and conductor David Caddick has been around since the very beginning – he was music director for a staged reading on Andrew Lloyd Webber's estate back in 1984. He's conducting the final performances on Broadway. "I simply don't know how I'll feel on the morning of the 17th of April," Caddick says. "At the moment, it's about maintaining what we have: keeping the show vibrant. I still give notes to the actors, to the orchestra. We will look to maintain every element of the production through to the very last note."

There are plans for some surprises at the final curtain call. Actor Richard Poole says the closing is bittersweet. " I was retiring anyway," he says. "So, I have a very enviable spot in my life in the fact that I had something to go to, which was nothing!" For the other 124 people employed by The Phantom of the Opera , it's time to find a new gig.

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The Phantom of the Opera marquee is shown above on April 13, 2023, at the Majestic Theater in New York City. The final performance will be on Sunday, April 16. Angela Weiss/AFP via Getty Images hide caption

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  • EJNMMI Phys
  • v.9; 2022 Dec

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3D printed anthropomorphic left ventricular myocardial phantom for nuclear medicine imaging applications

1 Division of Radiology and Imaging Science, Department of Medical Imaging, Faculty of Medicine, University of Debrecen, Nagyerdei krt. 98., Debrecen, 4032 Hungary

Laszlo Balkay

2 Division of Nuclear Medicine and Translational Imaging, Department of Medical Imaging, Faculty of Medicine, University of Debrecen, Nagyerdei krt. 98., Debrecen, 4032 Hungary

Kornel Kukuts

3 ScanoMed Nuclear Medicine Centers, Nagyerdei krt. 98., Debrecen, 4032 Hungary

Marton Miko

Attila forgacs.

4 Mediso Ltd., Laborc Utca 3., Budapest, 1037 Hungary

Gyorgy Trencsenyi

Aron k. krizsan, associated data.

Our phantom inserts are available in STL format in the supplementary material.

Anthropomorphic torso phantoms, including a cardiac insert, are frequently used to investigate the imaging performance of SPECT and PET systems. These phantom solutions are generally featuring a simple anatomical representation of the heart. 3D printing technology paves the way to create cardiac phantoms with more complex volume definition. This study aimed to describe how a fillable left ventricular myocardium (LVm) phantom can be manufactured using geometry extracted from a patient image.

The LVm of a healthy subject was segmented from 18 F-FDG attenuation corrected PET image set. Two types of phantoms were created and 3D printed using polyethylene terephthalate glycol (PETG) material: one representing the original healthy LVm, and the other mimicking myocardium with a perfusion defect. The accuracy of the LVm phantom production was investigated by high-resolution CT scanning of 3 identical replicas. 99m Tc SPECT acquisitions using local cardiac protocol were performed, without additional scattering media (“in air” measurements) for both phantom types. Furthermore, the healthy LVm phantom was inserted in the commercially available DataSpectrum Anthropomorphic Torso Phantom (“in torso” measurement) and measured with hot background and hot liver insert.

Phantoms were easy to fill without any air-bubbles or leakage, were found to be reproducible and fully compatible with the torso phantom. Seventeen segments polar map analysis of the "in air” measurements revealed that a significant deficit in the distribution appeared where it was expected. 59% of polar map segments had less than 5% deviation for the "in torso” and "in air” measurement comparison. Excluding the deficit area, neither comparison had more than a 12.4% deviation. All the three polar maps showed similar apex and apical region values for all configurations.

Conclusions

Fillable anthropomorphic 3D printed phantom of LVm can be produced with high precision and reproducibility. The 3D printed LVm phantoms were found to be suitable for SPECT image quality tests during different imaging scenarios. The flexibility of the 3D printing process presented in this study provides scalable and anthropomorphic image quality phantoms in nuclear cardiology imaging.

Performance measurements and optimization of nuclear medicine imaging systems involve the use of different phantoms to mimic human activity distributions [ 1 – 3 ]. Accurate anthropomorphic phantoms have been introduced to reveal quantitative inaccuracies and to detect the presence of image artefacts caused by inappropriate acquisition, reconstruction, and image processing [ 4 – 8 ]. Several of these phantoms are commercially available, generally with fixed size and geometry. 3D printing technology including direct ink writing [ 9 ], fused deposition modelling (FDM) [ 10 – 13 ], digital light processing (DLP) [ 14 ] or stereo-lithography (SLA) [ 15 ] offers large variety of possibilities to design custom-made geometrical and anthropomorphic phantoms [ 16 – 23 ]. A systematic review by Filippou et al. concludes that 3D printing methods can complete or replace commercially available phantoms in the fields of CT, MRI, PET, SPECT, US, and mammography imaging [ 24 ]. Several studies reveal 3D printed phantom solutions for nuclear medicine applications using real patient imaging data, including fillable multicompartmental torso in quantitative imaging analysis for 90 Y-DOTATATE radiopeptide therapy [ 25 ], fillable kidney phantom for 177 Lu SPECT reconstruction optimization [ 26 ], as well as tumor phantom set of various shapes for testing comparison of PET radiomics features in a multi-center approach [ 27 ]. Focusing on cardiac phantom solutions, Matsutomo et al. designed and printed a set of specific inserts to simulate different ischemic levels to complete the commercially available Myocardial SPECT Phantom HL (Kyoto Kagaku Co., Ltd., Kyoto, Japan) [ 28 ]. Grice et al. introduced a left ventricle (LV) cardiac phantom with simplified wall geometry containing low perfusion lesions within a non-anthropomorphic background container, printed from polylactic acid (PLA) material [ 29 ]. The endeavor of creating new cardiac phantoms is encouraged by clinically relevant, but unanswered methodological questions. The lack of geometrically appropriate cardiac phantom prevents the investigation of image artefacts and image processing failures attributed to the inhomogeneity of the cardiac wall thickness. 3D printing technology makes it possible to create the complex geometry of a real heart, which is not feasible with traditional manufacturing methods. This study aimed to determine whether creating a fillable, anatomically accurate 3D printed left ventricle myocardium (LVm) phantom segmented from a PET image volume of a real patient is feasible. The suitability of polyethylene terephthalate glycol (PETG) plastic for anthropomorphic LVm phantom production is demonstrated for the first time. The phantom insert was designed to be compatible with the commercially available Anthropomorphic Torso Phantom (DataSpectrum Co., Durham, NC). CT images are presented to confirm the reproducibility of 3D printing and phantom preparation. Furthermore, SPECT measurements were performed to demonstrate that the proposed phantoms give a complementary solution to the currently available phantoms in the field of nuclear cardiology imaging.

Materials and methods

Phantom design.

Input image data for the phantom design were extracted from an 18 F-FDG PET/CT study of a patient (age: 67 years; weight: 63 kg) without known coronary artery disease. Whole body PET/CT acquisition was performed on a GE Discovery MI system, using the local patient examination protocol (injected dose 220 MBq, 1.5 min acquisition time per bed position, 30% overlap between bed positions). Q.Clear reconstruction was applied with 384 × 384 matrix resulting in 1.82 × 1.82 × 2.79 mm voxel size (Fig.  1 upper row). The local ethics committee approved the use of patient data in this study.

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Three orthogonal views of reconstructed 18 F-FDG PET/CT image (upper row) and the 3D phantom design (bottom row)

For image segmentation process, we used the 3D Slicer software with basic functionality [ 30 ]. Images were cropped near to the area of the heart. Segmentation was done by applying the Otsu method with minimum and maximum threshold values obtained by visual inspection [ 31 ]. Irrelevant segmented voxels were deleted manually using the Erase tool. The 3D mask was saved in Standard Tessellation Language (STL) format with LPS (Left, Posterior, Superior) coordinate system and size scale of 1.0. The exported model was post-processing using Autodesk Meshmixer (Autodesk Inc., San Rafael, California, USA). The Plane Cut tool was used to make a plane surface on the left ventricle model from the direction of the left atrium perpendicular to the apex. A 0.5 mm offset distance was defined to create the model hollow, while solid accuracy and mesh density parameters were set to 512 in the Hollow tool. The size of the plain surface of the model was increased with the Extrude tool to make a 10 mm wide solid pedestal. In addition, with the Hollow and Extrude tools, a bubble trap was created. A phantom holder was also created in Trimble SketchUp Pro 2020 (Trimble Inc., Sunnyvale, California, USA) based on the distance and size of the pedestal holes of the commercially available Biodex Cardiac insert. This holder was merged with the previously created plane surface of the cardiac model in Meshmixer using Boolean Union method (Fig.  1 ). As a last step, two filling holes were designed, one of them through the bubble trap. Finally, with our primary purpose, two types of phantom models were designed: one as a representation of the healthy LVm with 190 ± 1 ml fillable volume (Fig.  1 lower row), and another mimicking transmural perfusion defective myocardium with a 20 × 30 mm oval solid plastic cold part (Fig.  2 ). The latter model has 165 ± 1 ml total fillable volume. These two phantoms will be referred to in the following as LVm healthy and LVm defective phantom.

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Multi-sectional image of the real 3D printed LVm defective phantom

3D printing

For slicing and creating the print plan, the Repetier-Host (Hot-World GmbH & Co. KG, Willich, Germany) software was used. The model was laid flat on its pedestal. Slicing parameters were the followings: 100% infill density; shell thickness was 0.4 mm with 0.2 mm layer height. No adhesion or support was generated for the 40 mm/s print speed. Retraction and cooling were enabled. Phantoms were printed using an Anet A8 FDM 3D printer (Anet Technology Co., Ltd., Shenzhen, People's Republic of China), build volume 220 × 220 × 240 mm, Marlin firmware, 0.4 mm nozzle diameter, with 3DJAKE PETG transparent filament. PETG thermoplastic was used for watertight and durability reasons and to avoid significant stringing, which is a well-known phenomenon in the case of other printing materials (e.g., PLA) [ 32 ]. Print bed and nozzle temperature were set to the mid-value of the manufacturer's recommended temperature ranges: 70 °C and 240 °C, respectively. The total 3D printing time was approximately 6 h for each model. The 0.4 mm nozzle diameter and 0.4 mm shell thickness print parameter give 0.4 mm real wall thickness to the printed phantoms. A few times, the phantom had clearly visible separate layers on the outer apex side after printing, in these cases, we used a soldering iron to melt them together. To prevent any further leakage between layers, Prisma Color Acrylic spray was applied to the outer surface on the printed phantoms as a finishing process. To assure as less leaking as possible, M5 size screws were 3D printed to tightly fit in the phantom filling holes (Fig.  3 ).

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Photographs of the real 3D printed LVm healthy phantom before ( a ) and after ( b ) a red food-dye diluted water filling

The described steps required to create LVm phantom models are shown in Fig.  4 . Our 3D phantom model is available in STL format in the supplementary material.

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Flowchart of steps required to create the LVm phantom models. Input data were an 18 F-FDG PET/CT study of a patient without known coronary artery disease. Three different software were used for model construction, and an additional program was applied to create the printing plan at different stages of the manufacturing process. Finished models were printed with an Anet A8 FDM 3D printer

Printing reproducibility, leaking test

Reproducibility of the phantom production was demonstrated with three separate printing series. Size, including the diameter of the pedestal and filling holes, was measured with a sliding calliper. Spiral CT scans with 120 kV, 120 mA x-ray settings, and voxel size of 0.625 × 0.703 × 0.703 mm were performed and evaluated on healthy phantoms filled with water to measure the accuracy of reproducibility. For the leakage test, watertight fillings were checked at least two times for each phantom (Fig.  3 ).

Phantom SPECT/CT measurements

99m Tc- water solution was mixed with red food-dye for better visual detection of bubbles and leakage. Decay corrected activity concentrations calculated to the acquisition start can be seen in Table ​ Table1 1 .

Decay corrected activity concentrations in kBq/ml applied for phantom preparations

In the first experiments, LVm healthy and defective phantoms were measured without additional scattering media ("in air”). The LVm healthy insert was also placed into the Anthropomorphic Torso Phantom for a second acquisition (“in torso”)

Measurements and reconstructions

Both LVm healthy and LVm defective phantoms were measured without additional scattering media (referring to as "in air” measurement). The LVm healthy insert was placed into the Anthropomorphic Torso Phantom for a second acquisition (referring to as "in torso” measurement). All imaging acquisitions were performed with identical acquisition parameters on a NaI(Tl) detector-based AnyScan® DUO FLEX SPECT/CT system (Mediso Medical Imaging Systems, Budapest, Hungary) equipped with Low energy High-Resolution (LEHR) parallel hole collimator. The different phantom arrangements on the SPECT/CT scanner bed can be seen in Fig.  5 . The routine clinical patient protocol for myocardial perfusion was selected, including the following parameters: 90 degrees scan arc, 64 projections, 128 × 128 matrix size, 140.5 keV energy with 20% window width, body contouring, and step and shoot mode. Additionally, a CT scan with 120 kV, 50 mA x-ray settings, and a voxel size of 2.50 × 0.977 × 0.977 mm was performed for attenuation correction purposes.

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"In air” measurement positioning of LVm phantom on the SPECT/CT scanner bed ( a ), and the “in torso” setup with the Anthropomorphic Torso Phantom, when the LVm phantom is placed at the location of the original heart insert ( b )

Data processing

Data were processed by the Mediso InterView™ XP application. Default Cardiac Perfusion Image reconstruction of Tera-Tomo™ 3D SPECT-Q was applied on the acquired raw data. Image size of 128 × 128 with 5.91 mm cubic reconstruction voxel size, 32 number of iterations and 4 subset size was used with CT-based attenuation and scatter correction. Polar maps with 17 segments were created for all three measurements and were applied to reveal similarities and differences. For this process, reorientations were performed by a medical expert physician with six years of experience. Polar maps of "in air" measurements of the healthy and defective myocardium phantoms were compared, to demonstrate how the defect alters the internal distribution of the radioactive solution inside the phantom. Since the "in torso” measurement represents more realistic scattering and attenuation conditions, the polar map of the "in air" measurement of the healthy myocardium phantom was compared to the polar map of the "in torso” measurement. Polar map graphs from the calculated percentage differences were also created for these evaluations.

After rigid registration of the high-resolution CT images of LVm healthy models, the phantoms present identical geometry within tight tolerances in shape (Fig.  6 ) and fillable volume.

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Representative sagittal view of the registered CT images of the three identical LVm healthy phantoms

The measured mean filled volume was 189.4 ml ± 1.4 ml, including the volume of the bubble trap. The printed LVm phantoms were easily refillable and were closed tightly, without any air bubbles or observable leakage during all of the presented measurements. Additionally, two phantoms were filled and stored for three months at room temperature, and no leakage or evaporation was detected. Reconstructed SPECT images of "in air” measurements reveal accurate uptake volumes (Fig.  7 ). Differences between defective and healthy phantom images were clearly visible on the sagittal views (Fig.  7 a, b) as well as on the 3D rendered image (Fig.  7 c, d). The defect appeared where it was planned during the phantom design.

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Uptake patterns of reconstructed SPECT images of LVm healthy and defective phantoms measured "in air” on three orthogonal views ( a , b ) and 3D rendered images of the two phantom realizations ( c , d )

Printed phantoms were compatible with the Anthropomorphic Torso Phantom to be assembled at the cardiac region. The reconstructed SPECT images revealed that the activity distribution of the LVm healthy phantom could be visualized in detail (Fig.  8 ).

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Reconstructed SPECT image of the LVm healthy phantom inserted in the Anthropomorphic Torso Phantom

Clear differences were found while analyzing the resulted polar maps of the three measurements of the "in air” and "in torso” arrangements (Fig.  9 ).

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Original (first column) and 17 segments (second column) polar maps of the three measurements

The polar map segment with the highest signal was found to be the basal anterolateral for LVm healthy and LVm defective "in air” measurements. On the other hand, the originally high signal mid-inferior region on the LVm healthy model was decreased significantly due to the artificial defect on the LVm defective model.

Polar map segment differences of the LVm healthy phantom measurements (first and last rows in Fig.  9 ) could originate from at least two sources. The radiopharmaceutical activity decayed compared to the "in air” case; therefore, the overall signal yield was expectedly lower. Moreover, the liver and the background in the torso phantom contained image distortions due to the spillover effect. All three polar maps have similar apex and apical region values.

The detailed relative perfusion percentage values of each region for all three measurements are summarized in Table ​ Table2, 2 , together with the relative percentage difference of measurement comparisons.

Polar map values for each measurement and related percentage differences

The last two columns show the relative % difference for each segment between "in air” measurements (column I. and II.) and between the LVm healthy phantom "in air” and "in torso” measurements (column I. and III.)

In the relative % difference columns (column IV. and V.), negative value means deterioration, while a positive represents an improved region. The values of the LVm healthy—LVm defective phantom comparison (column IV.), are in the range between − 24.7% and 10.6%, and 11 of the 17 segments have less than 5% value. The LVm healthy phantom "in air”–"in torso” comparison (column V.) has values between − 12.4%, and 10.2%, and 10 of the 17 segments have values less than 5%. The relative percentage differences were also depicted on differential polar maps (Fig.  10 ) based on column IV. and V. values of Table ​ Table2. 2 . Each color indicates 5 percentage steps. At the LVm healthy versus LVm defective phantom comparison, the deviations were higher than 5% deterioration concentrated on the four inferior regions where the artificial defect was designed. Two regions showed an improved signal ratio of more than 5%. Improvement and relapse regions in the case of LVm healthy phantom "in air” versus "in torso” comparison did not come from the nature of our phantom. As the concerning graph shows, the deviation is located in the basal edge regions, while the values are still around 5% except for the basal anterolateral region. This result and the 10.2% improvement in the apical region can be attributed to the uncertainty of the manual heart reorientation.

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Polar maps of the relative percentage differences for different LVm phantom measurements. Left panel: results of the LVm healthy phantom "in air” vs. "in torso” comparison. Right panel: results of the LVm healthy vs. LVm defective phantom comparison

While several conventional plastic phantoms are available to test the image quality and reliability of nuclear cardiology applications with SPECT [ 8 , 33 – 35 ], they still have some anatomical and size limitations. 3D printing technology has gained wide attention recently for creating anthropomorphic phantoms, due to its cost-effectiveness, fast production capability and the possibility for advanced and customized design in almost any shape even for nuclear cardiology applications [ 28 , 29 ]. In this work, two anatomically accurate LV myocardial phantom inserts were created from a real patient 18 F-FDG PET/CT study image set (Fig.  1 upper row). One represents the original healthy LV myocardium (Fig.  1 lower row), and the other includes an artificially added myocardium deficit (Fig.  2 ). Three LVm healthy phantoms were 3D printed to verify that there are no significant alterations in geometry (Fig.  6 .) and fillable volume (189.4 ml ± 1.4 ml). These phantom inserts were planned to be convenient and complementary solutions to the commercially available plastic phantoms used in nuclear cardiology. Bubbles in the myocardium volume of the LV phantoms could affect the distribution of the radioactive solution. The LV insert of the Anthropomorphic Torso Phantom has no bubble trap, while the 3D printed LVm inserts were designed to include one for bubble-free filling of the LV wall. Therefore, the imaging of our phantoms was not affected by the presence of bubbles in the artificial myocardium volume. Moreover, the conventional LV insert is available at a certain size in a geometrically simple shape [ 33 ]; however, our 3D printed LVm insert is scalable in size and results in a more realistic uptake pattern of the LV myocardial perfusion SPECT image (Fig.  7 ). The latter has particularly high significance in the case of testing optimal settings for image reconstruction algorithms to avoid artifacts. The LV myocardium wall has a significantly different cross-sectional diameter at the apex than other regions, and the iterative image reconstruction tends to reach accurate activity levels at different iteration numbers for the apex than to the LV walls [ 36 ] even in case of a geometrically simple LV phantom. This is more prominent when we consider the real anatomy of the LV with non-uniform wall thickness. Therefore, our phantom design is a good advocate to the geometrically simple LV phantoms to find optimal iteration number for a certain image reconstruction. In addition, the reduction in left ventricular apical tracer uptake called apical thinning or false apical defect [ 37 ] is frequently observed in myocardial perfusion imaging both in the field of PET [ 38 ] and SPECT imaging [ 39 , 40 ]. Among many potential causes, the diminished activity at the apex can be attributed to real anatomy [ 41 ] combined with the partial volume effect, as it is visible in our phantom model as well (Fig.  6 ). Another commercially available phantom called the Kyoto HL cardiac torso phantom (Kyoto Kagaku Co. Ltd., Kyoto, Japan) was used by Yoneyama et al. to test image reconstruction resolution recovery solutions to overcome ejection fraction (EF) limitations in case of pediatric patients [ 42 ]. However, with our method, two small size hearts can be printed from normal gated PET image sets in end-systole and end-diastole phases, and the EF measurement accuracy of different reconstruction methods can be tested [ 43 ]. It has to be mentioned that the commercially available AGATE phantom [ 8 ] can mimic simple heart motion and is compatible with the Anthropomorphic Torso Phantom. Therefore, gated SPECT acquisitions and EF calculation are possible; however, this phantom is also available only in adult patient size. The anatomically correct design of the LV myocardium is also important when comparing hybrid or ellipsoid sampling of polar map generation [ 44 ]. A set of printed phantoms with different clinically representative cases could be used to perform a comparison of existing nuclear cardiology software, since considerable differences are present in their performance [ 45 ]. We performed a representative set of SPECT image acquisitions using the 3D printed phantom inserts. Both LVm healthy and LVm perfusion defect phantoms were filled with 99m Tc, and SPECT acquisitions were performed on an AnyScan® DUO FLEX SPECT/CT system "in air”, without any scattering media and in the Anthropomorphic Torso Phantom including hot background and hot liver insert. The printed LVm models remained intact throughout the experiments, and the inserted 99m Tc radioactive solution did not dissolve into the torso phantom background chamber. Seventeen segments polar map analysis of SPECT images revealed that by comparing the LVm defective model to the LVm healthy one, a significant deficit in the radiopharmaceutical distribution appeared where it was expected (Fig.  9 ). The design process enables flexibility in placing the perfusion deficit with different numbers and shapes within the fillable wall of the phantom. Including the expected low perfusion segments at the deficit area, around 65% of the polar map segments had less than 5% deviation. When comparing the LVm healthy model, the "in torso” and "in air” measurements, 59% of all polar map segments had less than 5% deviation (Fig.  10 ). Concerning only the segments excluding the deficit area, neither comparison revealed more than 12.4% deviation, which difference could have originated most probably from phantom positioning error, the applied reconstruction method, and the well-known spill-over effect, especially in the case of the "in torso” phantom measurement. Beyond the flexibility and applicability of our method, this study has several limitations. We used an 18 F-FDG PET image set to create the phantom model; however, a more realistic model can be created with currently available PET myocardial perfusion traces such as 82 Rb-chloride, 13  N-ammonia or 18 F-flurpiridaz. We presented 3D printed phantoms in one LV size from a non-gated PET data of a healthy male patient. It would be beneficial to demonstrate phantom studies using healthy females and pediatric or even heart disease images as input data. On the other hand, the variety of these printable LVm phantoms should be limited to provide a few standardized shapes available to be downloaded and printed in any nuclear cardiology laboratory. The LV deficit designed and printed in the phantom was completely solid, representing scar burden. However, a fillable defect could be printed within the LV wall, and lower activity concentration can be inserted in that chamber to mimic ischemia. In this study, only the LV was segmented; however, the anthropomorphic nature of the phantom could be emphasized with a model including the right ventricle as well.

In this study, we proved that creating a fillable, anthropomorphic 3D printed phantom of the LV myocardium segmented from a real patient PET image volume is possible. SPECT images were acquired in different imaging scenarios proving the usefulness of the printed LVm phantoms. The flexibility of the 3D printing process presented in this study provides scalable and anthropomorphic image quality phantoms in nuclear cardiology imaging.

Acknowledgements

Not applicable.

Abbreviations

Author contributions.

AKK proposed the original idea, helped to find the right model design, and helped the polar map generation. LB, GT and AF helped to plan the measurements and analyzed the results from technical aspects. KK helped to complete the phantom measurements. MM analyzed the results from medical aspects. JK segmented, CAD designed, and 3D printed the presented LVm models as well as contributed to the measurements and wrote the manuscript draft. All authors read and approved the final manuscript.

Open access funding provided by University of Debrecen. The research was supported by the Thematic Excellence Programme (TKP2020-NKA-04) of the Ministry for Innovation and Technology in Hungary.

Availability of data and materials

Declarations.

The use of the 18 F-FDG PET/CT data of the corresponding anonym patient in this study was approved by the local ethics committee.

This study was performed as part of the first author’s PhD project. The other authors declare that they have no competing interests.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Should You Take the Left or Right Path in the Subway Tunnel in Cyberpunk 2077: Phantom Liberty? Answered

Which one is correct?

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After defeating the Chimera, you’ll find yourself in a subway tunnel with two branching paths in Cyberpunk 2077: Phantom Liberty . You now have to decide whether to take the left or the right path to reach your destination.

Which Way to Go in the Subway Tunnel in Phantom Liberty

Although Myers may make the event sound like an important decision, the two paths will eventually take you to the safe hideout Songbird has prepared . The only difference is their difficulties.

If you prefer the quicker and safer route , I suggest you take the left path. Although the road may seem to lead to a dead end, you can interact with the forklift on your right side to open a small tunnel. After you climb out using a ladder, you’ll find yourself in a hallway that leads to the elevator.

Activating the forklift in the left path in the subway tunnel in Cyberpunk 2077: Phantom Liberty.

On the other hand, the right path is a bit more challenging because of the two security cameras . You must be careful not to get recorded, or a group of enemies will chase you after you meet with Solomon Reed. However, if you get spotted, you can delete the recordings by accessing the computer in the control room after the broken pipe.

Personally, I recommend the left path so you can avoid the unnecessary puzzles and security cameras. You may get more loot by taking the right path, but none of them are particularly noteworthy, and you can easily get them in the future.

Now that you know which path to take in the subway tunnel , I recommend reading other Phantom Liberty articles on Twinfinite. If you’re curious about the new endings , you can check out our guide to find out the choices you need to make.

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About the author

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Gabriela Jessica

Gabriela has been a Freelance Writer for Twinfinite since 2023. She mainly covers Genshin Impact but also enjoys trying out new games. Her favorites are TOTK, Stardew Valley, RDR2, The Witcher 3, and RE4 Remake. Gabriela has a BA in English Literature from Ma Chung University and loves to spend her time reading novels and manga/anime.

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US and UK hint at military action after largest Houthi attack in Red Sea

  • Published 11 January
  • Israel-Gaza war

Two figures stand in a room of the HMS Diamond, looking out at a fiery scene

The US and UK have hinted they could take military action against Yemen's Houthi rebels, after they repelled the largest attack yet on Red Sea shipping.

Carrier-based jets and warships shot down 21 drones and missiles launched by the Iran-backed group on Tuesday night.

The UN Security Council passed a resolution on Wednesday demanding an immediate end to the Houthi attacks.

The text endorsed the right of UN member states to defend their vessels. The Houthis reacted scornfully to it.

Their spokesman Mohammed Ali al-Houthi called the resolution a "political game". They claim to be targeting Israeli-linked vessels, in protest at Israel's war against Hamas in Gaza.

The UN resolution demanded "that the Houthis immediately cease all such attacks, which impede global commerce and undermine navigational rights and freedoms as well as regional peace and security". Eleven nations voted for it, but Russia, China, Mozambique and Algeria abstained.

Earlier, the US and several allies warned of "consequences" for the Houthi attacks in the Red Sea. Asked about potential strikes in Yemen, UK Defence Secretary Grant Shapps said: "Watch this space."

The International Chamber of Shipping says 20% of the world's container ships are now avoiding the Red Sea and using the much longer route around the southern tip of Africa instead.

The Houthis said they targeted a US ship on Tuesday providing support to Israel. It was the 26th attack on commercial shipping in the Red Sea since 19 November.

  • Hard choices for the West in Red Sea stand-off
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  • Listen: Who are the Houthi rebels - BBC Sounds

The US military said Iranian-designed one-way attack drones, anti-ship cruise missiles and anti-ship ballistic missiles were launched from Houthi-controlled areas of Yemen at around 21:15 local time (18:15 GMT).

Eighteen drones, two cruise missiles and one ballistic missile were shot down by F/A-18 warplanes from the aircraft carrier USS Dwight D Eisenhower, which is deployed in the Red Sea, and by four destroyers, the USS Gravely, USS Laboon, USS Mason and HMS Diamond.

HMS Diamond shot down seven of the Houthi drones using its guns and Sea Viper missiles, each costing more than ÂŁ1m ($1.3m), a defence source said.

No injuries or damage were reported.

Later, Houthi military spokesman Yahya al-Sarea confirmed its forces had carried out an operation involving "a large number of ballistic and naval missiles and drones".

"It targeted a US ship that was providing support for the Zionist entity [Israel]," he said.

"The operation came as an initial response to the treacherous assault on our naval forces by the US enemy forces," he added, referring to the sinking of three Houthi speed boats and killing of their crews by US Navy helicopters during an attempted attack on a container ship on 31 December .

He added that the rebels would "not hesitate to adequately deal with all hostile threats as part of the legitimate right to defend our country, people and nation".

Mr Sarea also reiterated that the Houthis would continue to "prevent Israeli ships or ships heading towards occupied Palestine from navigating in both the Red Sea and the Arabian Sea until the [Israeli] aggression [on Gaza] has come to an end and the blockade has been lifted".

A spokesperson for UN Secretary General Antonio Guterres said he was "very concerned" because of the risks the situation posed to global trade, the environment and lives, as well as the "risk of the escalation of the broader conflict in the Middle East".

File handout photo showing HMS Diamond (14 October 2020)

Mr Shapps warned on Wednesday that the UK and its allies had "previously made clear that these illegal attacks are completely unacceptable and if continued the Houthis will bear the consequences".

"We will take the action needed to protect innocent lives and the global economy," he added.

Later, the defence secretary said in a TV interview that Iran was "behind so much of the bad things happening in the region" and warned the Islamic Republic and the Houthis that there would be "consequences" if the attacks on shipping did not stop.

Asked if there could be Western military action against Houthi targets in Yemen, or even targets inside Iran, he replied: "I can't go into details but can say the joint statement we issued set out a very clear path that if this doesn't stop then action will be taken. So, I'm afraid the simplest thing to say [is] 'watch this space'."

He was referring to a statement put out a week ago by the UK, US, Australia, Bahrain, Belgium, Canada, Denmark, Germany, Italy, Japan, Netherlands, New Zealand, South Korea and Singapore, who launched "Operation Prosperity Guardian" last month to protect Red Sea shipping.

They said the attacks posed "a direct threat to the freedom of navigation that serves as the bedrock of global trade in one of the world's most critical waterways".

It may not have had the bravado of Mr Shapps' "watch this space" warning, but US Secretary of State Antony Blinken was also clear in his condemnation of the incident.

A map showing the Bab al-Mandab strait, which sits between Yemen on the Arabian Peninsula and Djibouti and Eritrea on the African coast

Speaking to reporters at an airport in Bahrain during a Middle East tour, he was pressed by BBC North America correspondent Anthony Zurcher about whether it was time that talk of consequences turned to US action.

Mr Blinken responded that he did not want to "telegraph" a US military move, but that he had spent the past four days in the region warning the Houthis to cease their aggression.

They have not only refused, but after this latest strike have claimed they are specifically targeting US ships.

Almost 15% of global seaborne trade passes through the Red Sea, which is linked to the Mediterranean by the Suez canal and is the shortest shipping route between Europe and Asia.

The fear is that fuel prices will rise and supply chains will be damaged.

The Houthis say they have been targeting Israeli-owned or Israel-bound vessels to show their support for the Iran-backed Palestinian group Hamas since the start of the war in Gaza in October.

Formally known as the Ansar Allah (Partisans of God), the Houthis began as a movement that championed Yemen's Zaidi Shia Muslim minority.

In 2014, they took control of the capital, Sanaa, and seized large parts of western Yemen the following year, prompting a Saudi-led coalition to intervene in support of the international-recognised Yemeni government.

The ensuing war has reportedly killed more than 150,000 people and left 21 million others in need of humanitarian assistance.

Saudi Arabia and the US have accused Iran of smuggling weapons, including drones and cruise and ballistic missiles, to the Houthis in violation of a UN arms embargo. Iran has denied the allegation.

Related Topics

  • Global trade
  • Shipping industry
  • Grant Shapps
  • United States

More on this story

Red Sea attacks: 'Our costs have jumped 250%'

  • Published 3 January

Thomas O'Brien runs Boxer Gifts

UK says it will repel Houthi Red Sea attacks

  • Published 1 January

The HMS Diamond, off the coast of Scotland

US destroys Houthi boats after Red Sea hijack attempt

  • Published 31 December 2023

USS Eisenhower aircraft carrier

Who are the Houthis attacking Red Sea ships?

  • Published 3 days ago

Houthi fighters in Sana, Yemen. File photo 2019

BP pauses all Red Sea shipments after rebel attacks

  • Published 18 December 2023

Loading of huge oil tanker in a port in Jordan

IMAGES

  1. Multi-coloured phantom (left), reconstructed images of the 'fingers

    phantom left

  2. Photograph of compressed phantom (left), example x-ray image of phantom

    phantom left

  3. Rolls Royce Phantom Left View

    phantom left

  4. 3000Ă—3000-CODG-PHANTOM-LEFT-MIC-DOWN HR

    phantom left

  5. The Shepp-Logan phantom (left) and its corresponding sinogram (right

    phantom left

  6. Two-dimensional presentation of the emission phantom (left) and the

    phantom left

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