That Time the United States Tested Biological Warfare on its Own Citizens

For the residents of San Francisco, October 11, 1950 started out like any other day, with thick banks of autumn fog rolling in from the bay and across the city. By the afternoon, however, it became clear that something was seriously wrong. On that day alone, eleven patients were admitted to Stanford Hospital with pneumonia, fever, and serious urinary tract infections. One of them, a 75-year-old retired pipe fitter named Edward J. Nevin, died three weeks later. Tests revealed  the culprit to be Serratia marcescens, a bacterium so uncommon that not a single case of infection had been recorded in the entire history of San Fransisco. So baffled were the hospital’s doctors by this unusual cluster of infections that they reported the incident in a medical journal, though when no new cases appeared they dismissed it as a fluke. But unknown to the doctors and the residents of San Fransisco, the thick fogs that crept over the city that autumn carried a secret passenger: trillions of bacteria sprayed from a Navy ship sailing just offshore. Code-named Sea Spray, this operation was part of a top-secret Cold War project to test the city’s vulnerability to a potential Soviet biowarfare attack. But San Fransisco was far from alone; between 1949 and 1969, the U.S. Military deliberately exposed dozens of American cities and millions of ordinary citizens to potentially harmful bacteria and chemicals, all in the name of national security. This is the shocking story of one of the largest programmes of human experimentation in American history.

Biological warfare has long been a part of human conflict, from the medieval practice of catapulting infected corpses and rats into besieged cities to spread disease to the infamous use of smallpox-infected blankets during the 18th Century French and Indian War. But it was not until the late 19th Century, when scientists like Robert Koch and Louis Pasteur discovered the microorganisms that cause disease and how to cultivate them that the development of dedicated, effective biological weapons began in earnest. By the time of the First World War, Imperial Germany had built an extensive bioweapons programme, perfecting strains Anthrax and Glanders with which it planned to infect its enemies’ livestock and military draft animals. However, none of these weapons were ever deployed before the war ended. But the horrifying effects of the chemical weapons that had been used during the war – such as phosgene and mustard gas – left such an impression on world leaders that in 1925, 146 countries came together to draft the Geneva Protocol for the Prohibition of the Use of Asphyxiating, Poisonous, and Other Gases, and of Bacteriological Methods of Warfare. The treaty was signed by 38 nations including France, Great Britain, the Soviet Union, Japan, and the United States, though the latter two would not ratify it until the 1970s.

Over the next two decades, the majority of the Geneva Protocol’s signatories avoided developing biological weapons – with one major exception. In 1936, the Imperial Japanese Army established a biowarfare research centre outside the Chinese city of Harbin, in the Japanese puppet state of Manchukuo.  Run by General Shiro Ishii, the facility, known as Unit 731, would go on to commit some of the most horrific atrocities in modern history. In experiments that make the work of Nazi scientists like Dr. Josef Mengele look like the pinnacle of medical ethics, researchers at Unit 731 used local Chinese citizens as human guinea pigs, exposing them to deadly pathogens like Anthrax and Bubonic Plague before dissecting them alive without anaesthetic to study the effects of these diseases. Japanese aircraft also dropped bombs loaded with anthrax, plague, cholera, salmonella, and other agents on 11 Chinese cities, leading to tens of thousands of deaths.

While such horrors might seem like a unique product of Imperial Japan’s particular brand of extreme militarism, it was not long before the western powers, too, succumbed to the dark allure of biological warfare. Following the Nazi invasion of Poland in September 1939, the United Kingdom set up its own biowarfare program based at Porton Down in Wiltshire and Toronto in Canada, with research focusing on the weaponization of tularaemia, psittacosis, brucellosis, Q fever, and Anthrax – and for more on this, please check out our previous video Grosse Île – Canada’s Anthrax Island.

The Japanese attack on Pearl Harbour on December 7, 1941, also caused the United States to reverse its stance on biowarfare. In early 1942, U.S. Secretary of War Henry Stimson expressed concern to President Franklin D. Roosevelt regarding America’s vulnerability to biological attack. In response to this and growing pressure from the British, in November 1942 Roosevelt approved the creation of an American bioweapons program, overseen by the U.S. Army Chemical Warfare Service and centred at Fort Detrick, Maryland. By 1945, the US biowarfare program had succeeded in producing several tons of weaponized pathogens including anthrax and smallpox, though none were ever used in combat. American wartime policy dictated that such weapons were only to be used in retaliation or as a deterrent against enemy biological attacks, and in this the program was highly successful;  after the war, captured documents revealed that fear of American retaliation had convinced Nazi Germany to abandon its own biowarfare program.

The dawn of the Cold War brought a new sense of urgency to the U.S. bioweapons program, as intelligence obtained by the CIA revealed the existence of a vast Soviet biological warfare research program based in the city of Sverdlovsk in the Ural Mountains. Desperate to gain any possible advantage over the Soviets, the US Government went so far as to pardon the scientists of Japan’s Unit 731 in exchange for their data and expertise. Yet despite the Japanese’s extensive real-world experience in conducting biological warfare, many questions remained: which pathogens would cause the most damage? What was the most effective means of dispersal? How would pathogens spread in cities compared to the countryside? Which Soviet and American cities were most vulnerable to biological attack, and how could the latter be protected? Three potential methods were evaluated for answering these questions: first, small-scale testing using model cities in wind tunnels; second, full-scale testing using live pathogens in simulated cities; and third, full-scale testing using simulated pathogens in real cities. While wind tunnel tests by the British had yielded some useful results, the first two methods were quickly rejected – the first due to its technical limitations and the second due to the exorbitant cost of simulating an entire city. That left method #3: releasing simulated pathogens on real cities. The search thus began for American cities that could reasonably approximate Soviet population centres.

This proved more challenging than anticipated, for most regions which matched Russian cities in temperature and precipitation did not match them geographically – and vice-versa. In the end, however, eight cities were found to have the desired combination of climate, geography, and architecture: Oklahoma City, Kansas City, Omaha, Cincinnati, St. Louis, Chicago, and Winnipeg in Canada – with Minneapolis, St. Louis, and Winnipeg being identified as particularly suitable. Cities in California and Florida were also selected for tests involving coastal areas. To simulate biowarfare agents, researchers chose four different kinds of bacteria: Serratia marcescens, Bacillus globigii, Bacillus subtilis, and Aspergillus fumigatus. Chosen for their similarity to real biowarfare agents like anthrax and tularaemia, these bacteria were also readily found in nature and easy to grow – indeed, Serratia marcescens is responsible for the pink film often found growing in bathtubs and toilets. Chemical simulants were also used, including zinc cadmium sulphide, a powder whose small particle size and fluorescent glow made it ideal for tracking the airborne dispersal of infectious agents. At the time, all these simulants were considered harmless to humans. Despite this, for reasons of security and obtaining the most accurate results possible, the residents of the targeted cities would not be informed that the tests were taking place. Thus began one of the most ethically fraught chapters in the history of American military research.

The first bioweapons test on U.S. soil took place in August 1949, when agents of Camp Detrick’s Special Operations Division released inert bacteria into the ventilation system of the Pentagon. Larger-scale operations soon followed, including Operation Sea Spray. Between September 20 and 27, 1950, a U.S. Navy minesweeper sailed just off of San Fransisco Bay spraying a mixture of Serratia marcescens and Bacillus globigii from large onboard hoses. Meanwhile, 43 monitoring stations throughout the city recorded the dispersion of the bacteria. According to Leonard J. Cole, author of the book Clouds of Secrecy, the data revealed that:

“Nearly all of San Francisco received 500 particle minutes per liter. In other words, nearly every one of the 800,000 people in San Francisco exposed to the cloud at normal breathing rate (10 liters per minute) inhaled 5000 or more particles per minute during the several hours that they remained airborne.”

Similar tests were conducted off the coast of South Carolina, Georgia, and Florida, while between 1953 and 1975 the UK’s Chemical Defence Experimental Establishment at Porton Down carried out the Dorset Biological Warfare Experiments, spraying a combination of zinc cadmium sulphide and Bacillus globigii off the coast of Southwestern England.

In 1965, as part of the Pentagon’s Project 112, American researchers released Bacillus globigii at the National Airport and Greyhound Terminal in Washington, DC. More than 130 passengers were exposed, spreading the simulant bacteria to 39 cities in 7 states over the next two weeks. The following year, Bacillus Subtilis was released into the New York subway system by dropping lightbulbs filled with bacteria onto the tracks. These bacteria also spread quickly through the subway lines, leading the official Army report on the experiment to conclude:

“Similar covert attacks with a pathogenic disease-causing agent during peak traffic periods could be expected to expose large numbers of people to infection and subsequent illness or death.”

The largest of these experiments, however, was Operation LAC, which took place between 1957 and 1958. Short for “Large Area Coverage”, LAC evaluated the feasibility of covering large areas with biowarfare agents by releasing them from aircraft. Using Fairchild C-119 Flying Boxcar cargo aircraft, LAC released hundreds of tons of zinc cadmium sulphide over 33 rural and urban areas in the midwestern United States and Canada, with ground stations monitoring the dispersion of the fluorescent powder. The tests revealed the aerial dispersion method to be extremely effective, with the simulant travelling up to 1,900 kilometres from where it was dropped.

As covered in our previous videos That Time US Scientists Injected Plutonium Into People Without Their Knowledge and The Appalling Tuskeegee Syphilis Experiment, human medical experimentation in the United States has tended to have a strong racial component, often targeting poor black communities and other vulnerable groups. Operation LAC was no exception. Starting in the mid-1950s, the Army began spraying zinc cadmium sulphide powder from motorized blowers mounted atop Pruitt-Igoe, a massive public housing block in St. Louis inhabited almost entirely by poor blacks. As part of the Army Chemical Corps’s St. Jo program, simulant was also sprayed from aircraft and trucks in St. Louis, Minneapolis, and Winnipeg – again, mostly in poorer neighbourhoods. As the sprayers could not be easily hidden, residents were told that they produced an invisible smoke screen that would shield the cities from Soviet radar.

Between 1949 and 1969, the U.S. Armed Forces conducted a total of 239 open-air biowarfare experiments on 66 American and Canadian cities, 80 of which used live bacteria. The program was only halted due to a 1969 directive by President Richard Nixon calling for the elimination of the United States’ entire stockpile of biological warfare agents – the destruction of which was completed by 1973. While U.S. Government officials hoped that all records of the human biological warfare experiments would be destroyed along with the weapons themselves, in 1976 Newsweek reporter Drew Fetherston uncovered classified documents revealing many of the secret tests. This in turn led the San Fransisco Chronicle to uncover and report on the Operation Sea Spray experiments of September 1950. In light of these revelations, in 1977 the federal government formed the U.S. Senate Subcommittee on Health and Scientific Research in 1977 to investigate allegations of unethical experimentation.

While the U.S. Army believed that the biowarfare simulants used it its live experiments were harmless to humans, it is now known that in large enough doses Serratia marcescens and Bacillus globigii can cause serious infections. Indeed, it is now believed that the release of these bacteria over San Francisco permanently altered the microbiome of the region, leading to an epidemic of heart valve infections in hospitals and other serious infections among intravenous drug users throughout the 1960s and 1970s. And in 2004, a string of infections caused by an influenza vaccine was traced to Serratia marcescens contamination at the Chiron Corporation’s factory in Alameda, California. However, it is now believed that the 11 cases of Serratia marcescens-induced urinary tract infections on October 11, 1950 were unrelated to Operation Sea Spray. As Army officials testified in the 1977 Senate hearings, all 11 patients had recently undergone minor surgeries and the outbreak was confined to a single hospital, indicating that the source of infection lay inside the hospital itself. Nonetheless, in 1977 the surviving family members of Edward J Nevin, who had allegedly died as a result of the 1950 experiments, sued the federal government for negligence and financial and emotional harm, with Nevin’s grandson, Edward J. Nevin III, stating:

“My grandfather wouldn’t have died except for that, and it left my grandmother to go broke trying to pay his medical bills.”

Unfortunately, the U.S. District Court in San Francisco ruled against the Nevins, claiming there was insufficient evidence that the bacteria used in the test were responsible for Edward J. Nevin’s death. Undeterred, the Nevins took their case all the way to the U.S. Supreme Court, with the trial finally taking place on March 16, 1981. In his opening statement, Edward Nevin III, himself a lawyer, questioned the legal and ethical validity of the biowarfare experiments, stating:

“On what basis of law does the U.S. government of the United States justify the dispersion of a large collection of bacteria over the civilian population in an experiment…without informed consent?”

Unfortunately for Nevin, the government had assembled a formidable team of legal representatives and expert witnesses, including attorney John Kern, who proceeded to deny every one of Nevin’s arguments. The strain of bacteria that had killed Nevin’s grandfather, Kern argued, was of an entirely different strain than the one used in the Operation Sea Spray experiments. Furthermore, in tests conducted at Fort Detrick in 1940, volunteers exposed to Serratia marcescens had suffered nothing more serious than coughing, redness of the eyes, and fever, with symptoms lasting no longer than four days. Kern then dramatically hammered home is point by thrusting his pen into the air and declaring:

“Every atom in this pen could decide right now to rise up about six inches and turn around 180 degrees. That would be about as likely to happen as the bacteria killing someone.”

One of Kern’s witnesses, a doctor for the biological warfare unit at Fort Detrick, concurred, chillingly stating:

“The strain [wasn’t] pathogenic, [and] I would still spray SF again today.”

Kern then proceeded to dismantle Nevin’s arguments regarding the legality of the biowarfare tests, making the extraordinary claim that the government needed no permission to experiment on the public without their consent or knowledge. While the 1946 Federal Tort Claims Act gives the public the right to sue the Federal Government, this right is suspended in cases where the Government is “performing appropriately under policy.” According to Kern, this exception applied to activities carried out in the interest of national security – including spraying civilians with bacteria.

Though Nevin put up a valiant fight, he knew it was all over when Kern called his final witness to the stand: General William Creasy, commander of the U.S. Army biological warfare unit. In his testimony, Creasy stated that not only was obtaining informed consent from the public not necessary, it was not desirable, stating:

“I would find it completely impossible to conduct such a test trying to obtain informed consent. I could not have hoped to prevent panic in the uninformed world in which we live in telling them that we were going to spread non-pathogenic particles over their community; 99 percent of the people wouldn’t know what pathogenic meant.”

The trial only got more belligerent from there, with Creasy berating Nevin for his alleged lack of respect for military officials and even trying to start a fistfight during recess. In the end, however, the Supreme Court sided with the Government and refused to overturn the San Francisco District Court ruling. The Nevins’ four-year battle for justice ended in defeat.

Meanwhile, doubts have been raised regarding the safety of the zinc cadmium sulphide simulant used in the U.S. Army’s LAC experiments.While at the time the compound was considered harmless, it is now known that cadmium is a powerful human carcinogen and in high concentrations can cause damage to the lungs, kidneys, and other organs. After learning of the stimulant-spraying experiments in St. Louis, in 2012 sociology professor Lisa Martino-Taylor claimed to have examined medical records and discovered a significant spike in cancer rates in the decades following the tests. However, no further evidence has emerged to confirm this link, with the U.S. National Research Council’s official study on the matter concluding:

“After an exhaustive, independent review requested by Congress, we have found no evidence that exposure to zinc cadmium sulfide at these levels could cause people to become sick.”

Thus, without further, independent study, the true impact of the LAC experiments may never be known. But regardless of the morally dubious nature of these experiments, it appears that they did, in fact, yield genuinely useful results. As Leonard Cole, adjunct professor of political science at Rutgers University explains:

“We learned a lot about how vulnerable we are to biological attack from those tests. I’m sure that’s one reason crop dusters were grounded after Sept. 11: The military knows how easy it is to disperse organisms that can affect people over huge areas.”

Today, the knowledge gained through these tests is used for purely defensive purposes. In 1972, 109 countries including the United States signed the Convention on the Prohibition of the Development, Production, and Stockpiling of Bacteriological (Biological) and Toxin Weapons and on Their Destruction. Since then, the U.S. military has not maintained any offensive or defensive biological warfare capability – not officially, anyway. Yet accusations persist that human testing continued in secret. For example, in 2019 Republican representative for New Jersey Chris Smith alleged that from 1950-1975, the U.S. Army released ticks infected with Lyme disease to test its effect on the American public. If true, this would mean that the U.S. Government knew about Lyme disease long before its official discovery in 1982. However, no convincing evidence has yet emerged to back up Smith’s claims.

Along with other secret military projects of the era, such as the CIA’s MKULTRA mind-control experiments and the University of California’s plutonium injection studies, the U.S. Army’s biological warfare tests represent one of the great ironies of the Cold War. For while these experiments were ultimately intended to protect the public and preserve American institutions, in the end they succeeded only in harming millions of American citizens, shattering their faith said institutions, and proving the old adage: “just because you’re paranoid doesn’t mean they’re not out to get you.”

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Expand for References


Toxicologic Assessment of the Army’s Zinc Cadmium Sulfide Dispersion Tests, National Research Council, 1997,


Salter, Jim, The Army Sprayed St. Louis With Toxic Aerosol During a Just revealed 1950s Test, Business Insider, October 4, 2012,


Carlton, Jim, Of Microbes and Mock Attacks: Years Ago, The Military Sprayed Germs on U.S. Cities, The Wall Street Journal, October 22, 2001,

Military Once Used SF Fog For Simulated Germ-Warfare Attack, Exposing 800,000 To Harmful Bacteria, CBS Bay Area, July 10, 2015,


The US Has a History of Testing Biological Weapons on the Public – Were Infected Ticks Used Too? The Conversation, July 22, 2019,


Crockett, Zachary, How the US Government Tested Biological Warfare on America, Priceonomics, October 30, 2014,


Secret Testing in the United States, The American Experience,


Barnett, Antony, Millions Were In Germ War Tests, The Guardian, April 21, 2002,


The Dorset Biological Warfare Experiments 1963-1975,

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