Allegations that the United States military used biological weapons in the Korean War (June 1950 – July 1953) were raised by the governments of the People's Republic of China, the Soviet Union, and North Korea. China and North Korea also made allegations that US forces used chemical weapons. Subsequent scholars are split about the truth of the claims.

The claims were first raised in 1951, and claimed the use of anti-personnel, anti-crop, and anti-animal pathogens, including the causative agents of anthrax, plague, smallpox, and typhoid fever. The story was covered by the worldwide press and led to a highly publicized international investigation in 1952. Secretary of State Dean Acheson and other American and allied government officials denounced the allegations as a hoax. The United States biological weapons program operated from 1942 to 1973. Following the surrender of Japan, the US military conducted a cover-up of the Japanese biological warfare program.

Background Until the end of World War II, Japan operated a covert biological and chemical warfare research and development unit called Unit 731 in Harbin (now China). The unit's activities, including human experimentation, were documented by the Khabarovsk War Crime Trials conducted by the Soviet Union in December 1949. Although the US government at the time described the Khabarovsk trials as "vicious and unfounded propaganda", it was later revealed that the accusations made against the Japanese military were correct. The US government had taken over the research at the end of the war and had then covered up the program. Leaders of Unit 731 were exempted from war crimes prosecution by the United States and then placed on the payroll of the US.

On 30 June 1950, soon after the outbreak of the Korean War, the US Defense Secretary George Marshall received the Report of the Committee on Chemical, Biological and Radiological Warfare and Recommendations, which advocated urgent development of a biological weapons program. The biological weapons research facility at Fort Detrick, Maryland was expanded, and a new one in Pine Bluff, Arkansas, was developed. In December 1951, as the war turned against the United States, the Defense Secretary ordered early readiness for using biological weapons offensively.

Allegations The Chinese and North Koreans made allegations, both publicly and at the United Nations, of U.S. use of biological warfare. In a May 8, 1951 cablegram from the Foreign Minister of the Democratic People's Republic of Korea, Pak Hon-yong, to the President of the UN Security Council. Pak cited documents captured from South Korean forces that described plans "for the use of bacteria in diversionary work on the territory of North Korea." One plan, allegedly drawn up by "Section 3 of the Intelligence Bureau of the Staff of the South Korean Army," described spreading infectious material in "Army kitchens," "police mess-rooms," "city reservoirs," and "houses of army, government and party leaders," and other areas. These plans also called for spreading bacteria in eleven different towns, as well as against "units of the People's Army." In addition, Pak charged that "several areas" had been "infected with small-pox sickness 7 to 8 days after their liberation from American occupation." Pak said there were smallpox cases in Pyongyang and five outlying DPRK provinces, amounting to at least 3,500 smallpox cases, allegedly due to deliberate spread of variola virus. Ultimately, these charges were not pursued, but when in 1952 the Communists took up the germ war charges again, they did refer back to the 1951 smallpox cases.Endicott, Stephen; Hagerman, Edward The United States and Biological Warfare: Secrets from the Early Cold War and Korea; Bloomington, IN: Indiana University Press; 1998; pp. 97-98Winchester, Simon; The Man Who Loved China: The Fantastic Story of the Eccentric Scientist Who Unlocked the Mysteries of the Middle Kingdom; New York: Harper Collins; 2008; pp. 199–200McCormack, Gavan; "Korea: Wilfred Burchett's Thirty Year's War"; in Kiernan, Ben (ed.); Burchett: Reporting the Other Side of the World, 1939-1983; London: Quartet Books; 1986; pp. 202–203.Harris, Sheldon H.; Factories of Death: Japanese Biological Warfare, 1932–45, and the American Cover-up; Taylor & Francis; 2002 General Matthew Ridgway, United Nations Commander in Korea, denounced the initial charges as early as May 1951. He accused the communists of spreading "deliberate lies". A few days later, Vice Admiral Charles Turner Joy repeated the denials. French journalist André Stil, who was a member of the French Communist Party and editor of the socialist newspaper L'Humanité, was arrested for publishing and repeating these allegations.

On 28 January 1952, the Chinese People's Volunteer Army headquarters received a report of a smallpox outbreak southeast of Incheon. From February to March 1952, more bulletins reported disease outbreaks in the area of Chorwon, Pyongyang, Kimhwa and even Manchuria. The Chinese soon became concerned when 13 Korean and 16 Chinese soldiers contracted cholera and the plague, while another 44 recently deceased were tested positive for meningitis.Zhang 1995, p. 182. Although the Chinese and the North Koreans did not know exactly how the soldiers contracted the diseases, the suspicions soon fell on the Americans.

On 22 February 1952, Pak Hon-yong made a formal allegation that American planes had been dropping infected insects onto North Korea. He added that the Americans were "openly collaborating with the Japanese bacteriological war criminals, the former jackals of the Japanese militarists whose crimes are attested to by irrefutable evidence. Among the Japanese war criminals sent to Korea were Shirō Ishii, Masaji Kitano, and Jirō Wakamatsu." Pak's accusations were immediately denied by the US government. The accusation was supported by eye-witness accounts by Australian reporter Wilfred Burchett and others.Knightley, Phillip; The First Casualty: The War Correspondent as Hero and Myth-maker from the Crimea to Kosovo, revised ed.; London: Prion; 2000; p. 388.

In June 1952, the United States proposed to the United Nations Security Council that the Council request the International Red Cross investigate the allegations. The Soviet Union vetoed the American resolution due to extensive US influence inside the Red Cross, and, along with its allies, continued to insist on the veracity of the biological warfare accusations.

In February 1953, China and North Korea produced two captured U.S. Marine Corps pilots to support the allegations. Colonel Frank Schwable was reported to have stated that: "The basic objective was at that time to get under field conditions various elements of bacteriological warfare and possibly expand field tests at a later date into an element of regular combat operations." Schwable's statement said that B-29s flew biological warfare missions to Korea from airfields in American-occupied Okinawa starting in November 1951. Schwable's statement was obtained following months of torture and abuse at the hands of his captors, according to the US military. Other captured Americans such as Colonel Walker "Bud" Mahurin made similar statements.

Despite the allegations of torture, a United Press report in February 1954 described how U.S. flyers had been instructed by their superior officers that if they were captured on missions they could, according to Marine Major Walter R. Harris, "tell anything you want to." Similarly, Marine Colonel—and Medal of Honor recipient—R. E. Galer, who, like Schwable, had been shot down over Korea, said, according to an Associated Press report, that "the Strategic Air Command and other Air Force units briefed their men to tell more than their names, rank and serial numbers.”

At the Winter 1954 Marine Corps Board of Inquiry hearing on Colonel Frank Schwable's alleged collaboration with his Chinese captors, the Commandant of the Marine Corps admitted "the conflicting nature of existing instructions relative to the conduct of members of the armed forces while held as prisoners of war." Meanwhile, several paragraphs on what exact instructions had been given to the flyers were redacted in the publication of the Inquiry's findings as published in The New York Times.

Upon release the prisoners of war repudiated their confessions, which they said had been extracted by torture. However, the retractions happened in front of military cameras after the United States government threatened to charge the POWs with treason for cooperating with their captors. Kenneth Enoch, one of the former POWs who retracted his confession, was tracked down in 2010 by Al Jazeera reporters. He denied being ill-treated or indoctrinated by the North Korean or Chinese guards or playing any personal role in biological weapons attacks, but said "they send it with you."

International Scientific Commission

When the International Red Cross and the World Health Organization ruled out biological warfare, the Chinese government denounced them as being biased by the influence of the US, and arranged an investigation by the Soviet-affiliated World Peace Council.Guillemin, Jeanne; Biological Weapons: From the Invention of State-sponsored Programs to Contemporary Bioterrorism (M1, via Google Books), Columbia University Press; 2005; pp. 99–105; . The World Peace Council set up the "International Scientific Commission for the Facts Concerning Bacterial Warfare in China and Korea" (ISC). This commission had several distinguished scientists and doctors from France, Italy, Sweden, Brazil and Soviet Union, including renowned British biochemist and sinologist Joseph Needham. The commission's findings included dozens of eyewitnesses, testimonies from doctors, medical samples from the deceased, bomb casings as well as four American Korean War prisoners who confirmed the US use of biological warfare. On 15 September 1952, the final report was signed, stating that the US was experimenting with biological weapons in Korea.Winchester, Simon; The Man Who Loved China: The Fantastic Story of the Eccentric Scientist Who Unlocked the Mysteries of the Middle Kingdom; New York: Harper Collins; 2008; pp. 203–208.

The report suggested a link to the World War II Japanese germ warfare Unit 731. Former Unit 731 members Shirō Ishii, Masaji Kitano, and Ryōichi Naitō, as well as other Japanese biological warfare experts, were often named in the allegations. Former members of Unit 731 were linked initially, by a Communist news agency, to a freighter that allegedly carried them and all equipment necessary to mount a biological warfare campaign to Korea in 1951. The commission placed credence on allegations that Ishii made two visits to South Korea in early 1952, and another one in March 1953. The official consensus in China was that biological weapons created from an American-Japanese collaboration were used in the Korean episode. Citing the claims Ishii had visited South Korea, the report stated: "Whether occupation authorities in Japan had fostered his activities, and whether the American Far Eastern Command was engaged in making use of methods essentially Japanese, were questions which could hardly have been absent from the minds of members of the Commission."[Report of the International Scientific Commission for the Investigation of the Facts Concerning Bacterial Warfare in Korea and China (Peking and Prague, 1952), p. 14]

The International Association of Democratic Lawyers (IADL) publicized these claims in its 1952 "Report on U.S. Crimes in Korea", as did US journalist John W. Powell.

The Sams mission