History's most evil experiments: From Josef Mengele sewing twins together and Japan's 'plague bombs', to sending Soviet soldiers through an atomic blast-zone and the CIA's LSD mind control tests

Throughout the 20th century, the world's biggest powers inflicted horrific pain on their own citizens in the form of mass human experimentation.

Less than 100 years ago Nazi Germany, Imperial Japan, the Soviet Union and the United States were all conducting experiments, each with their own sick motivation.

While the Nazis were working to advance their grotesque racial policies, Japan was testing the limits of human capability in their own death camps. 

As a continuation of such research, the US went on to launch a mind control programme that was only discovered decades later. The same can be said for another US study into syphilis, which still haunts marginalised communities.

Furthermore, in the early days of the Cold War as fears mounted over atomic war, the Soviet Union conducted a terrifying test to establish how it could win on the battlefield in the event of nuclear strikes across Europe.

To this day, the number of people who were killed in such experiments is unknown - and is likely to never be truly uncovered.

Here, MailOnline looks at some of the most horrifying mass human experiments carried out in the 20th century.

Nazi medical experiments

Perhaps the most infamous experiments carried out on humans were undertaken by the Nazis during the Holocaust and the Second World War.

From 1933 to 1945, Adolf Hitler and other powerful Nazi leaders - such as Heinrich Himmler - spearheaded a campaign to 'cleanse' German society of those viewed as biological threats to the ideal Aryan race.

The racial policies developed by Nazi Germany determined that Jews, Roma and Slavs - including Poles, Czechs, Russians and Serbs - were 'racially inferior sub-humans', and should therefore be removed from society.

Nazi officials enlisted physicians and medically trained geneticists, psychiatrists, and anthropologists to develop their policies on race and to try and create what would have effectively been Nazi super soldiers.

This began with mass sterilisation in hospitals, with around 400,000 Germans being sterilised in the 1930s - and ended in the near total destruction of European Jewry and the murder of millions of people - all in the name of purifying the Aryan race.

As millions of Jews and people of other races were rounded up across the Third Reich and sent to their deaths at Nazi death camps, doctors were tasked with carrying out experiments on a selection of those prisoners.

There were 15,754 documented victims of these evil practices, but the true number is believed to be much higher. While many survived the atrocities (a quarter of documented victims were killed), survivors suffered severe and permanent injuries.

According to the United States Holocaust Memorial Museum, Nazi experiments fell into three categories: to facilitate the survival of military personnel, to test drugs and medical treatments, and to advance Nazi racial and ideological goals.

Experiments aimed at increasing the survival of Nazi troops saw physicians conduct high altitude tests on prisoners to determine the maximum height at which German air force crews could parachute to safety.

A low pressure chamber was used to simulate conditions of altitudes up to 68,000 feet. Of the 200 subjects, 80 died outright, while it was rumoured that German SS doctor Sigmund Rascher performed vivisections on patients who initially survived.

Scientists also carried out freezing experiments on prisoners in an attempt to better understand how soldiers could survive in the cold after Axis armies suffered on the Eastern Front from a lack of preparedness for the freezing weather.

Victims were submerged in tanks of cold water to determine how long it would take them to die. Some were submerged for up to three hours.

Others were forced to stand in the open air with temperatures as low as minus six degrees Celsius, many screaming in pain as their bodies froze.

The Nazi medics also tested methods to warm subjects, with one assistant later testifying that some victims were 'thrown into boiling water for rewarming'. 

Experiments were also conducted to study methods on how to make seawater drinkable. Subjects were deprived of food and only given filtered seawater, with some growing so desperate for water that they licked freshly mopped floors.

Tests were also carried out on patients to develop drugs and treatment methods for injuries and illnesses suffered by German military personnel in the field.

At the Sachsenhausen, Dachau, Natzweiler, Buchenwald, and Neuengamme concentration camps, scientists used prisoners to test immunisation compounds and antibodies for the prevention of contagious diseases - including malaria, typhus, tuberculosis, typhoid fever, yellow fever, and infectious hepatitis.

Sigmund Rascher experimented with the effects of Polygal, a substance designed to aid blood clotting. Subjects were given a Polygal tablet and then shot through the neck and chest, or had limbs amputated without anaesthesia.

At Ravensbrück concentration camp, doctors experimented with bone, muscle and nerve regeneration, as well as bone transplantation from one person to another.

In these horrific experiments, victims had bones, muscles and nerves removed without anaesthesia, suffering from agony, mutilation and disability.

Physicians at the camp also tested newly developed sulfa (sulfanilamide) drugs.

They would mutilate patients to mimic battlefield wounds and infect wounds with bacteria to test the effectiveness of sulfonamide and other drugs.

The Nazis also carried out head injury experiments (in which a prisoner would be struck over the head repeatedly to test the effects, malaria experiments (which saw victims were deliberately infected with malaria and treated with drugs) and experiments to test the effects of various poisons.

Some victims died as a result of the poison, while others were killed immediately for physicians to conduct autopsies on a poisoned patient.

Poison tests were heavily documented and photographed by the Nazis.

Test subjects were also deliberately exposed to mustard gas for physicians to find the most effective treatment for mustard gas burns.

Similar experiments were carried out on phosphorus burns.

 The third and final category of human experimentation according to the US Holocaust Memorial Museum was the Nazis working to advance Nazi racial ideology and eugenics.

As research by academics sought to establish 'Jewish racial inferiority', other doctors worked to find ways in which the Aryan gene pool could be reinforced.

One such doctor was Josef Mengele at Auschwitz - aka The Angel of Death - perhaps the best known Nazi physician due to his experiments on twins.

From 1943–1944, his experiments were of particular interest to Nazi high commands as one twin could serve as a test subject with the other as the control, and it was also hoped that his research could discover how Nazis could reproduce more twins.

Mengele's cruel tests included the amputation of healthy limbs, deliberately infecting twins with diseases such as typhus, blood transfusions from one twin to the other and sewing twins together to create conjoined twins.

Eva-Mozes Kor, a survivor, claimed Mengele cross-transfused the blood of opposite sex twins to change their respective sexes, experimented on twins' genitals and attempted to attach the urinary tract of a seven-year-old girl to her own colon. 

Most twins died during Mengele's procedures, but if any survived, they would be killed and dissected for comparative autopsies.

Out of the 1,500 twins subject to the experiments, only around 200 survived.

Nazis also carried out sterilisation and fertility experiments, looking for a way to sterilise millions of people with minimum time and effort.

The targets of these experiments included Jewish and Roma populations. 

Surgery, various types of drugs and the use of X-ray were all tested, and thousands of victims were sterilised. Many were killed in the Nazi's pursuit.

In all, hundreds of doctors took part in Nazi killings and experiments on prisoners, and a doctor was present at all mass killings for legal reasons.

While roughly ten per cent of the German population became Nazi Party members by 1945, that figure was more than half of all German doctors.

Doctors working for the Nazi government saw the extermination of patients as the correct solution for mental illness and those they saw as genetically defective.

'The participation in the 'betrayal of Hippocrates' had a broad basis within the German medical profession. Without the doctors' active help, the Holocaust could not have happened,' wrote E Ernst in the International Journal of Epidemiology.

It took many years for some of the perpetrators to be brought to justice, if ever.

After the war, the crimes of the Nazi physicians were tried at what became known as the Doctor's Trial, while the abuses ultimately led to the Nuremberg Code of medical ethics. However, some doctors changed their names or fled Germany. 

Of the 23 doctors who stood trial at the Nuremberg Trials, 15 were convicted and seven were condemned to death.

Other doctors, such as Walter Schreiber, were covertly moved to the US during 'Operation Paperclip' in 1951.

Unit 731

Thousands of miles away from Nazi Germany, another imperial power was also carrying out heinous human experiments during the Second World War.

Thousands of prisoners entered the Japanese Imperial Army's Unit 731 - code-named the Kwantung Army's Epidemic Prevention and Water Purification Department - but never left, and were instead treated as human guinea pigs for depraved tests. 

Innocent men, women and children were killed in the most savage ways imaginable - dissected alive, infected with deadly viruses, raped and used for target practice with flamethrowers and even 'plague bombs'.

Overseeing all of these unspeakable crimes was Unit 731's Dr Death - Shiro Ishii - a charismatic surgeon and ultra-nationalist fanatic who is considered the architect of the now notorious death camp's atrocities.

Ishii, an army surgeon, established the biological warfare research unit in 1936 to study germ warfare, weapons capabilities and the limits of the human body.

He did so with significant government funds and the blessing of Emperor Hirohito, who approved the policies and methods set out for him.

In the town, the Japanese occupiers would not permit the construction of buildings high enough to glimpse the violence within the compound walls.

'None of the people around here had any idea what the real purpose of the facility was,' researcher Han Xiao said.

'It was the secret of all secrets - trains could only pass with their curtains drawn; the Air Force would shoot down any plane that came too close.'

Once set up, military police began to hunt down victims for the unit's experiments - many of whom were Chinese civilians including children.

The army also sent Russian, British and American POWs there.

Inmates were deliberately kept healthy and fed a diet of rice, meat, fish and even alcohol on occasion, so their bodies would be in good condition for the experiments.

Ishii and his staff employed gruesome tactics to secure specimens of certain organs for their experiments, according to historian Sheldon H Harris.

'If Ishii or one of his co-workers wished to do research on the human brain, then they would order the guards to find them a useful sample,' Harris wrote in his book titled 'Factories of Death'.

'A prisoner would be taken from his cell. Guards would hold him while another guard would smash the victim's head open with an axe. His brain would be extracted and rushed immediately to the laboratory. 

'The body would then be whisked off to the pathologist, and then to the crematorium for the usual disposal.'

Vivisections were also common practice, with former workers revealing what they saw - and even did themselves - decades later.

A former medical assistant, a farmer in his 70s who wanted to remain anonymous, told the New York Times in 1995 about the first time he cut open a live man.

'The fellow knew that it was over for him, and so he didn't struggle when they led him into the room and tied him down,' he said.

'But when I picked up the scalpel, that's when he began screaming.

'I cut him open from the chest to the stomach, and he screamed terribly, and his face was all twisted in agony. He made this unimaginable sound, he was screaming so horribly. But then finally he stopped.

'This was all in a day's work for the surgeons, but it really left an impression on me because it was my first time.'

Inmates also had limbs amputated and organs removed before the depraved surgeons reattached their body parts - often in the wrong place - to see the effects.

Germ warfare experiments were also a key part of Unit 731, with Ishii and his henchmen breeding lethal strains of viruses to wipe out the Chinese population.

Enough germs were created to kill everyone on earth many times over, according to reports, with 300 kilos of plague bacteria produced every month, 500 kilos of anthrax, and nearly a tonne of dysentery and cholera.

Children were fed chocolates laced with anthrax and biscuits infected with plague, while older inmates were given typhoid-infected dumplings and drinks.

Thirty teenagers from Harbin died after being given typhoid-contaminated lemonade, according to a report in the Sydney Morning Herald looking back at the horrors of what it called 'Asia's Auschwitz'.

Another atrocity saw men infected with syphilis and then forced to rape other inmates, with the stated purpose to see how the disease was transmitted. 

What's more, women were forcibly impregnated for them and their babies to be used in these experiments.

Although babies were born in Unit 731, none survived.

The hundreds of prisoners who were alive when Japan surrendered at the end of the war were murdered and buried as the imperial army tried to cover up its crimes.

Former commanders, who were sworn to secrecy, recognised the savagery of their own operations, but many said they felt numb to them as they carried them out.

Sakaki Hayao, who headed Unit 731's Lin Kou branch, detailed an 'extremely cruel' experiment conducted at the Anda field in his testimony to the Shenyang special military tribunal in 1956.

He said he saw people tied to wooden poles and exposed to anthrax through bombs filled with the bacteria that were dropped from aircraft or detonated at close range. 

The cruel experiment was conducted just a few months before Japan's surrender. 'It was an especially brutal act,' he said.

Three days after the atomic bomb was dropped on Nagasaki, soldiers were ordered to bury the burnt bones of murdered inmates to conceal the crimes.

Soviet forces invaded the former Manchuria in August, and Unit 731's staff retreated back to Japan, with many never revealing their crimes and going on to enjoy relatively normal lives.

One of the most disturbing elements is the consequences many of these horrific experiments - unique in scientific history - had for medical knowledge today, with some of the experimental data gleaned from the human test subjects making advances in modern medical understanding.

Ishii was said to be particularly proud of Unit 731's discoveries about the mechanism of frostbite.

The effects of various remedies were tested on their frostbitten limbs, which were also painfully heated up by the sick surgeons as they tested the effects on victims as young as three years old.

General Okamura, a friend of Ishii, proudly noted in his memoirs 'I did not know the details of the medical advances he made, but after the war Ishii told me that his work produced more than 200 patents.'

As if the experiments at Unit 731 were not enough, similar units were set up in conquered cities such as Nanking (Unit 1644), Beijing (Unit 1855), Guangzhou (Unit 8604) and Singapore (Unit 9420) - expanding the program.

After the war, Supreme Commander of the Occupation Douglas MacArthur handed Ishii immunity in the name of the United States - and all members of the units - in exchange for all of the results of the experiments.

The veil drawn over his crimes meant that despite the horrors he inflicted, Ishii was allowed to live out his days peacefully - dying from throat cancer in 1959.

Totskoye nuclear exercise

With the conclusion of the Second World War, the United States and the Soviet Union found themselves in a nuclear arms race.

The US had already demonstrated the terrifying capability of nuclear weapons by dropping two on Japan in 1945 - one on Hiroshima and a second on Nagasaki - and in doing so had signalled that a new power had arrived on the world stage.

The gauntlet had been thrown down, and - as ideological differences drove a wedge through US-Soviet relations, and fears of a third World War intensified - the Soviet Union knew that it needed to catch up with its Western advisory.

The first Soviet nuclear weapons test came in 1949, and the country would test another 17 over the next five years, including ten in 1954.

But one test that year was different from the others.

In September 1954, the Soviet Army carried out an aerial detonation of a 40-kilotonne RDS-4 nuclear bomb in Russia's southern Orenburg Oblast.

The bomb was twice as powerful as the one dropped on Nagasaki nine years earlier by the United States to effectively end the Second World War, and the blast was near 45,000 Red Army troops, as well as 10,000 civilians.

This would later become known as the Totskoye nuclear exercise.

It was the first exercise to utilise nuclear weaponry in preparation for a nuclear war and to put troops on the ground in the vicinity of a nuclear blast.

Soon after the blast, with the mushroom cloud still rising, the 45,000 Soviet soldiers were ordered to march through the area around the hypocenter (or ground zero). 

The area had been chosen especially because it shared some similarities with the Fulda Gap, found in West Germany, where it was planned that Soviet forces would drive through NATO lines in the event of war against the West.

Soviet Leaders wanted to know how close living things could get to a nuclear blast, and whether its forces could be sent through a gap opened by the devastation of a nuclear bomb dropped on the battlefield.

They also wanted to know if troops could fight on a battleground immediately after it was hit by an atomic bomb. 

However, this meant testing how troops coped in the blast zone itself. 

What's more, although locals were ordered to evacuate the surrounding region, many chose to stay. Houses burned down, and the number of people who were killed, maimed or became ill as a result of the exercise may never be determined.

The exercise only came to light in the wake of the fall of the Soviet Union in the 1990s. According to a 1995 New York Times article, a film of the test from Soviet military archives shows that the Soviets exposed their troops to a level of radiation 10 times higher than the maximum permitted in a whole year for US troops.

The film also shows that troops were exposed to high levels of radiation for an extended time without sufficient protection against the effects.

To test the immediate effects on living things, livestock were also placed around the site of the detonation - many of which were wiped out. 

In the film, the narrator says that animals within 1,200 yards died, while others that were around 4,000 miles away were injured and burned.

The narrator says that an hour after the explosion, radiation measurements of 50 roentgen showed that 'it is possible to attack through the explosion region.'

Soldiers were seen staging a mock battle through the plains, still smoking - the air thick with dust. 

A Soviet veteran, speaking in a documentary about the exercise, said: 'Some, the majority even, had no protective clothing, and besides it was impossible to use gas masks' in 115-degree temperatures.

The narrator adds: 'The offensive troops, using protective equipment, passed through this territory without any damage to their health.'

However, at the end of the day-long exercise, veterans said soldiers did not change their contaminated clothes or weapons, although they were interviewed afterwards to test their morale following the experiment.

Many became sick soon after they participated in the war games.

The soldiers had been carefully selected from Soviet military servicemen.

They were told they would be taking part in an exercise involving a new type of weapon, sworn to secrecy, and promised three months' salary.

However, according to reports, many of those who were in the region on the day went on to suffer from cancer, birth defects, child mortality, hematologic disease, and chromosomal abnormalities.

The Soviet soldiers are not the only troops to have been involved in nuclear weapons tests in the years following the Second World War.

The US, UK and France all also sent troops to witness blasts, albeit from a greater distance than the Soviet soldiers in 1954.

One British veteran who witnessed the detonations described his memory of witnessing an atomic blast to Motherboard in 2022.

'It was utter devastation. If I was looking at you now, I would see all your bones. You would see all the blood vessels. All I saw was this rising, colossal fireball going up and thunder, lightning, you name it,' David Hemsley, who experienced atomic bomb blasts at the age of 18, told the publication. 'I think it was too much for some people - some of them were crying, asking for their mum. It was awful.' 

MK-Ultra

While the previous examples may suggest that human experimentation is a horror confined to totalitarian regimes, that was not the case with MK-Ultra - a top-secret, illegal programme undertaken by the American Central Intelligence Service (CIA).

The objective of the programme was to develop procedures and drugs that could be used in interrogations to weaken suspects and force confessions out of them through brainwashing and psychological torture.

This was after the CIA had become convinced that the communists had discovered a drug that would allow them to control human minds - and so the American agency set about testing its own drug that could be weaponized against enemies.

MK-Ultra began in 1953 and ran for an astonishing two decades until 1973, but only came to light in 1975 when it was revealed by the Church Committee of the United States Congress and Gerald Ford's commission on CIA activities.

Until then, however, the public was blissfully unaware of the shocking experiments going on in the name of national security, in which US and Canadian citizens were illegally used as the CIA's unwitting test subjects.

US interests in drug-related interrogation experiments actually began around a decade before the start of the MK-Ultra programme, in 1943. 

Then, the Office of Strategic Services began developing a 'truth drug' that would produce 'uninhibited truthfulness'.

It has been argued that these American operations were the 'continuation' of Nazi experiments carried out on victims of the Holocaust, in which German doctors aimed to develop a truth serum which would 'eliminate the will' of a suspect.

To back up this argument, American historian Stephen Kinzer - who extensively studied the programme - cited the several German scientists who were hired by the US as part of the aforementioned Operation Paperclip.

In 1947, the US Navy initiated Project CHATTER, which saw the testing of the drug LSD on human subjects, and in 1950 the CIA initiated a series of interrogation projects involving human subjects.

This began with the launch of Project Bluebird in 1950, renamed to Project Artichoke in 1951 - the objective of which was to test whether a person could be made to carry out an involuntary attempted assassination.

This was the predecessor of the MK Ultra programme, which began in 1953.

On April 13, 1953, CIA chemist Sidney Gottlieb became America's mind control czar.

He was handed permission to 'launch and conduct experiments at will.' 

The project was given a new cryptonym - MK- ULTRA - and under that dark umbrella a myriad of gruesome 'subprojects' were launched. 

The scope of the project was broad, and its activities were carried out under the guise of research across 80 institutions aside from the military. These included colleges, universities, hospitals, prisons, and pharmaceutical companies.

Gottlieb headed up the project, and some of his research was covertly funded by universities and research centres, Kinzer said.

Others were conducted in American prisons and detention centres across Japan, Germany and the Philippines.

Kinzer's research found subjects endured psychological torture ranging from electroshock 'therapy' to high doses of LSD.

'Gottlieb wanted to create a way to seize control of people's minds, and he realised it was a two-part process,' Kinzer told NPR in 2019.

'First, you had to blast away the existing mind. Second, you had to find a way to insert a new mind into that resulting void. 

'We didn't get too far on number two, but he did a lot of work on number one.'  

Gottlieb's team consisted of 'obsessed chemists, coldhearted spymasters, grim torturers, hypnotists, electro-shockers and Nazi doctors,' Kinzer said. in his 2019 book: Poisoner in Chief: Sidney Gottlieb and the CIA Search for Mind Control.

A 'safe house' was established in New York City's Greenwich Village where unsuspecting victims of MK-Ultra were lured and doped with LSD.

They were a new kind of 'expendable' for Gottlieb – mostly drug users and petty criminals who wouldn't be missed and wouldn't complain.

In the nine years of MK-ULTRA's existence, Gottlieb sponsored projects in prisons across the country in which inmates would be bribed by the promise of better cells, even heroin, for submitting to hideous tests.

In Atlanta Federal Penitentiary prisoners were told they were part of a study to find a cure for schizophrenia and dosed with LSD every day for 15 months.

One of the 'volunteers' was James 'Whitey 'Bulger. He later told of hallucinations and nightmares that made him think he'd lost his mind.

In another project children between the ages of six and eleven, who'd been diagnosed with schizophrenia, were given LSD every day for six weeks.

Brothels were set up and wired to study how the combination of sex and drugs impacted men's willingness to divulge secrets.

Mentally ill children were fed cereal laced with uranium and radioactive calcium. A secret CIA clinic was set up inside a Washington Hospital and while little is known of the work done there it was all on patients who were terminally ill.

Doctors were paid enormous stipends to administer drugs to their unwitting patients at Gottlieb's behest.

Doctors such as Paul Hoch, the New York psychiatrist visited by professional tennis player Harold Blauer in 1952 for depression following his divorce.

Blauer was injected with a concentrate of mescaline derivative which was without explanation or warning.

The treatment continued despite his protests that it was giving him hallucinations. On January 8, 1953 he was injected with a dose fourteen times more potent than the previous ones. He died eight minutes later.

By the mid-fifties CIA-sponsored 'subprojects' were being conducted in institutions including, Massachusetts General Hospital, Mount Sinai Hospital, the Universities of Pennsylvania, Minnesota, Denver, Illinois, Oklahoma, Rochester, Texas and Indiana as well as Berkeley, Harvard, Columbia, MIT, Stanford, Baylor, Emory, George Washington, Vanderbilt, Cornell, John Hopkins New York University. At one point the agency attempted to buy the world's entire supply of LSD. 

Gottlieb himself was known to spike colleagues' coffee and drinks with the tasteless, odourless drug.

Watching his colleagues get high, Kinzer notes, 'he would sometimes dance a jig.'

MK-ULTRA's work was so secretive that only two people really knew what was going on – Gottlieb and his deputy Richard Lashbrook.

They wrote as little down as possible and prided themselves on the fact that the right hand, quite deliberately, didn't know what the left hand was doing. 

But at one staff retreat in a lodge in Virginia Gottlieb did something that would come back to haunt him and play a part in his downfall.

Frank Olson was another brilliant chemist who had been recruited by Baldwin and worked closely with Gottlieb. The two travelled around the world together witnessing 'special interrogations' under the influence of drugs often made by Olson.

In the fall of 1953 Gottlieb slipped LSD into Olson's punch. Nine days later Olson plunged thirteen stories from a Manhattan hotel room.

In the intervening days, he had asked to leave the program. He had been paranoid, disoriented and depressed.

Gottlieb would always maintain that he sent Olson on his fateful trip to Manhattan, accompanied by Lashbrook to receive psychiatric treatment and that his death was suicide or an accident.

Olson's family believe that his desire to leave the CIA's most clandestine project led to his murder, and decades later Olson's son had his father's body exhumed and a new autopsy performed.

The pathologist noted that although Olson landed on his back the skull above his left eye was disfigured. He changed the manner of death from suicide to misadventure.

That same year that Olson died, Gottliebe wrote a CIA handbook on assassination was written. One of the methods he recommended was 'the contrived accident.'

He wrote, 'The most efficient accident… is a fall of 75 feet or more onto a hard surface. It will usually be necessary to stun or drug the subject before dropping him. A rock or heavy stone will do… Blows should be directed to the temple.'

Tuskegee syphilis experiment

MKUltra was not the only human experimentation programme carried out on US soil.

Between 1932 and 1972, the United States Public Health Service (PHS) and the Centers for Disease Control and Prevention (CDC) conducted a study on a group of nearly 400 African American men with syphilis.

The US Public Health Service called it 'The Tuskegee Study of Untreated Syphilis in the Negro Male', but the world would soon come to know it simply as the 'Tuskegee Study' - one of the biggest medical scandals in US history, an atrocity that continues to fuel mistrust of government and health care among Black Americans. 

The stated purpose of the study was to observe the effects of the sexually transmitted infection when left untreated - despite the disease being entirely treatable long before the experiment came to an end.

For four decades, the US government had denied hundreds of poor, Black men treatment for syphilis so researchers could study its effects on the body. 

By the time the study did finally close down, more than 100 people had died.

The PHS began the study in 1932 in collaboration with the historically black Tuskegee University (then the Tuskegee Institute), based in Alabama.

Starting in 1932, the Public Health Service - working with the famed Tuskegee Institute - began recruiting Black men in Macon County, Alabama. 

Researchers told them they were to be treated for 'bad blood,' a catch-all term used to describe several ailments, including anaemia, fatigue and syphilis.

Treatment at the time consisted primarily of doses of arsenic and mercury. 

In exchange for their participation, the men would get free medical exams, free meals and burial insurance - provided the government was allowed to perform an autopsy on them if they died.

Eventually, more than 600 men were enrolled, of which 399 of them had latent syphilis. A control group of 201 were not infected.

What they were not told was that about a third would receive no treatment at all - even after penicillin became available in the 1940s.

Instead, they were provided disguised placebos, ineffective methods of treatment and diagnostic procedures as treatment for the so-called 'bad blood'.

What's more, subjects were initially told that the experiment would only last six months. However, it was extended for 40 years, running until 1972.

By then, 28 patients had died directly from the infection, while 100 died from complications related to syphilis. Furthermore, 40 of the patients' wives were infected, and 19 children were born with congenital syphilis.

The study has since been called 'arguably the most infamous biomedical research study in US history' and continues to haunt communities today.

The story was broken by the Associated Press after 29-year-old reporter Jean Heller was handed an envelope containing details by Edith Lederer.

Inside were documents telling a tale that, even today, staggers the imagination.

Lederer had been working at the San Francisco AP bureau four years earlier, in 1968, when she met Peter Buxtun. Three years earlier, while pursuing graduate work in history, Buxtun had taken a job at the local Public Health Service office in 1965.

There, he was tasked with tracking venereal disease cases in the Bay Area.

In 1966, Buxtun had overheard colleagues talking about a syphilis study going on in Alabama. He called the Communicable Disease Center, now the Centers for Disease Control and Prevention, and asked if they had any documents they could share.

He received a manila envelope containing 10 reports, he told The American Scholar magazine in a story published in 2017. 

He knew immediately that the study was unethical, he said, and sent reports to his superiors telling them so, twice. 

The reply was essentially: Tend to your own work and forget about Tuskegee. 

'I knew that I could not do this,' Lederer said during a recent interview. 'AP, in 1972, was not going to put a young reporter from San Francisco on a plane to Tuskegee, Alabama, to go and do an investigative story.'

But she told Buxtun she knew someone who could.

At the time, Heller was the only woman on the AP's fledgling Special Assignment Team, a rarity in the industry. Lederer delivered the documents to her.

The government refused to talk about the study, so Heller set about asking people working in medical fields if they had heard anything of the project in Alabama.

Finally, one of her sources recalled seeing something about the syphilis study in a small medical publication. She headed to the DC public library.

There, she found an obscure medical journal that had been chronicling the study's 'progress.' 'Every couple of years, they would write something about it,' she recalled. 'Mostly it was about the findings - none of the morality was ever questioned.'

Armed with the journal, Heller went back to the PHS, who caved, and the AP bureau agreed to publish the story. Nearly four months later, the study was halted.

The government established the Tuskegee Health Benefit Program to begin treating the men, eventually expanding it to the participants´ wives, widows and children. 

A class-action lawsuit filed in 1973 resulted in a $10 million settlement.

The last participant died in 2004, but the study still casts a long shadow over the nation. Many African Americans cited Tuskegee in refusing to seek medical treatment or participate in clinical trials. 

It was even cited more recently as a reason not to get the COVID-19 vaccine.