18 Cover-Ups in History That Only Came Out Decades Later
A gripping journey through history’s buried secrets, this list unveils 18 shocking cover-ups, from secret experiments to government lies, that only came to light decades later.
- Alyana Aguja
- 6 min read
History is full of secrets so explosive that they were hidden for decades before emerging finally into the light. From government secrets and faked wars to medical deception and covered-up atrocities, these 18 cover-ups demonstrate how truth can be postponed but never suppressed. Each is a heart-stopping examination of the potency of secrecy — and the human spirit it requires to out it.
1. The Tuskegee Syphilis Study (1932–1972)
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For 40 years, the U.S. Public Health Service misled hundreds of Black men in Alabama by monitoring the course of untreated syphilis without their consent. The men were informed that they were receiving treatment, but they were denied access to penicillin even after it became the standard treatment. The public only became aware of the study in 1972, and national outrage ensued, leading to stricter ethical standards in medical research.
2. Operation Northwoods (1962)
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Declassified records showed that the U.S. Department of Defense came up with a scheme to stage terrorist acts on American soil to justify a war with Cuba. The plans entailed hijacking aircraft, sinking Cuban refugee boats, and staging bombings — all blamed on Fidel Castro. President Kennedy turned down the plan, but the public didn’t know about it until 1997.
3. The Manhattan Project (1942–1946)
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The U.S. government kept the development of the atomic bomb absolutely secret, involving more than 130,000 individuals at several locations. Even Vice President Truman was not told until FDR passed away in 1945. The world discovered the complete extent of the project only after the bombings of Hiroshima and Nagasaki.
4. MK-Ultra (1953–1973)
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The CIA experimented with mind control on unsuspecting American and Canadian citizens, administering LSD, hypnosis, sensory deprivation, and torture. The aim was to create interrogation methods and potential brainwashing techniques in the Cold War era. It was kept secret until a 1975 Senate inquiry and the publication of declassified documents in 1977.
5. The Katyn Massacre (1940)
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Approximately 22,000 Polish officers and intelligentsia were killed by the Soviet NKVD, but for decades Moscow blamed Nazi Germany. Western Allies, knowing of Soviet culpability, remained silent throughout WWII to preserve the alliance. The Soviet Union did not officially acknowledge guilt until 1990.
6. Project 112 and SHAD (1962–1973)
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Thousands of American troops were unwittingly exposed to chemical and biological agents during clandestine Cold War experiments. The tests were denied by the Department of Defense for decades, even to ill veterans who experienced unexplained diseases. The programs were not officially confirmed until 2002.
7. Unit 731 (1930s–1945)
Image from The Guardian
This secret Japanese biological warfare division carried out deadly human experiments in occupied China, such as vivisections and germ warfare experimentation. Following WWII, U.S. officials gave immunity to numerous participants in return for their research information. The reality emerged gradually through survivor accounts and declassified documents years later.
8. COINTELPRO (1956–1971)
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The FBI quietly undermined civil rights organizations, anti-war activists, and left-wing groups under this counterintelligence program. Methods involved infiltration, psychological operations, and false arrests. The public became aware of COINTELPRO only after a 1971 burglary at an FBI field office and ensuing congressional hearings.
9. The Gulf of Tonkin Incident (1964)
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President Johnson used purported North Vietnamese attacks on American warships as a pretext for increasing American involvement in Vietnam. Years later, declassified NSA documents showed that the second attack probably never occurred. The incident had been fabricated to help win congressional authorization for war.
10. Operation Paperclip (1945 onwards)
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During WWII, the United States secretly transported more than 1,600 German scientists who were members of the Nazi Party to work within American aerospace and weapons projects. Wernher von Braun, who assisted in constructing NASA’s Saturn V rocket, was among them. It remained a classified operation until the 1970s.
11. The Downwinders and Nuclear Fallout (1940s–1960s)
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The U.S. had more than 200 above-ground nuclear tests, some in Nevada, exposing local communities, “downwinders,” to radioactive fallout. Government agencies minimized or denied the health effects for decades. It wasn’t until the 1990s that there was compensation and public recognition.
12. The My Lai Massacre (1968)
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American troops murdered more than 500 unarmed Vietnamese civilians, including children and women, in the village of My Lai. Military leaders initially tried to cover up the massacre as a legitimate battle. Whistleblower testimony and investigative reporting finally revealed the atrocity in 1969, but some of the details took decades to come to light.
13. The Dreyfus Affair (1894–1906)
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Alfred Dreyfus, a French army officer who was Jewish, was wrongly accused of spying and jailed. Proof later emerged that another officer was guilty, but the military authorities covered this up to save their image. It wasn’t until more than a decade of public protest and a second trial that Dreyfus was vindicated.
14. The CIA’s Role in the 1953 Iranian Coup
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Britain and the United States staged a coup to install Iran’s democratically elected Prime Minister Mohammad Mossadegh and reinstate the Shah. The CIA dismissed involvement for years, labeling it an internal matter of Iran. Only in 2013 did the United States officially admit the role through the declassification of documents.
15. The Pentagon Papers (1945–1967)
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The Pentagon Papers, released in 1971 by whistleblower Daniel Ellsberg, demonstrated that several U.S. administrations had deliberately deceived the public regarding the Vietnam War. The papers indicated that officials secretly questioned victory while publicly declaring progress. It took over two decades of war and protest before such facts became widely known.
16. The Bohemian Grove Tapes (1980s–1990s)
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Although not a “cover-up” in the traditional sense, Bohemian Grove’s activities — a secluded annual elite retreat — remained hidden from the public for decades. Leaked footage and testimony in the 1990s showed strange rituals, political debates, and the attendance of influential leaders. It questioned extragovernmental and extracorporate influence on policy and corporate decisions.
17. Bayer and the HIV-Infected Hemophilia Meds (1980s)
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In the early 1980s, Bayer knowingly distributed clotting drugs for hemophiliacs contaminated with HIV overseas, even after it withdrew them from the U.S. market. Thousands were infected in Asia and Latin America. Internal documents that attested to knowledge of the risk weren’t uncovered until lawsuits in the 1990s.
18. The Bhopal Disaster’s True Death Toll (1984)
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A poisonous gas leak from a Union Carbide pesticide factory in Bhopal, India, killed thousands on the spot and poisoned more than half a million. The company minimized the disaster, and the Indian government did not seek full responsibility. It was not until many years later that independent researchers and activists exposed the full extent of the tragedy and cover-up.