Unit 731 was pardoned internationally post-WWII solely because they provided advantages to the world’s medical status quo. Controversially, the methodology used to conduct research was unethical, violating statutes of international law. 

When examining such atrocities, society popularly turns to the Nanking Massacre, otherwise labelled the “Rape of Nanking”, the mass ravaging of Chinese citizens capitulated by soldiers of the Japanese Imperial Army after its seizure of Nanjing, China on December 13th, 1937 (Encyclopaedia Britannica, 2025). An estimated 100,000 to over 300,000 fatalities are subject to debate, with the destruction of Nanjing ordered by Matsui Iwane, the commanding general of the Japanese Central China Front Army that captured the city. Ordered by Matsui, Japanese soldiers over the next coming weeks carried out numerous mass executions and thousands of rapes, alongside the looting and burning of the surrounding towns and city. Shortly after World War II, Matsui and Tani Hisao, a lieutenant general who personally participated in such acts, were found guilty of war crimes by the International Military Tribunal for the Far East and were thus executed (Encyclopaedia Britannica, 2025). 

There existed, however, another atrocity, one which was not so fortunate to meet similar legal retribution due to its alleged contributions to medical advancement in the eyes of the once opposition to the Japanese, the Allies. Unit 731, a biological and chemical warfare experimentation unit infamous for human experimentation during its existence in World War II, consisted of thousands of men, women and children subjected as marutas* or “logs” to experiments conducted at Pingfang, China alone (PAE, n.d.). Unit 731 raises the question: 

                            To what extent can we call scientific discovery ethical if the benefits of that scientific discovery help humanity,                 but the methodology to attain such results violates intrinsic human rights?

The hellish inner workings of a biological and chemical warfare experimentation unit

At the time of Unit 731’s inception, biological and chemical weapons were not new to warfare, with Japanese testing on human subjects unparalleled at the time, nor was the Japanese contribution to medical science. Three decades earlier, a U.S. Army doctor, Lewis Livingston Seamen, observed colleagues who attended to the Imperial Japanese Army during the Russo-Japanese War of 1904-1905 (Barrett, 2018). Dr Seamen was exceedingly impressed with his medical brethren, stating: 

                           “The history of warfare for centuries has proven that in prolonged campaigns, the first, or actual enemy, kills                   20 per cent of total mortality in the conflict, while the second, or silent enemy (disease), kills 80 per cent.” (Barrett, 2018)

Seamen stated Japan to be the first country to recognise that the greatest enemy in war was not the opposition but preventable disease, “a foe more treacherous and dangerous, as found lurking in every camp” (Barrett, 2018). 20 years later, Japan signed the Geneva Convention, stipulating a prohibition of biological and chemical warfare. 

Other men reasoned, with justification, that such weapons should be banned by civilised nations. However, a specialist in bacteria and related fields, Dr Colonel Shiro Ishii, saw the aforementioned Geneva Convention prohibition as an opportunity. If something were drastic enough to have been outlawed, it was reasoned to be effective. Hence, he began a sustained effort to establish a military arm within the Japanese Army, aiming to develop weapons based on biology. 

Ishii believed himself to be beyond reproach, and as a visionary, driven to break scientific ground to help Japan defeat its foes. Ishii exhorted his team of physicians to violate the physicians’ code:

“A doctor’s God-given mission is to challenge all varieties of disease-causing microorganisms; to block all roads of intrusion into the human body; to annihilate all foreign matter resident in our bodies; and to devise the most expeditious treatment possible….” 

(Barrett, 2018)

Beginning of the establishment of Unit 731

To convince the Imperial Army’s senior figures to back his efforts, Ishii’s case was built around finance, avoiding the moral obligations of the Geneva Convention and instead arguing that bacteria and gas were a less expensive alternative to warfare development. Nationalism in Japan in 1930 further created a climate receptive to Ishii’s ideas of biological weapon development. 

Resultantly, the Mukden incident of September 1931 was a ruse to justify a takeover of Manchuria – now encompassing the entirety of present-day northeast China and parts of modern-day Russia's Far East – a historically significant land rich with living space and natural resources fruitful for Japanese expansionist ambitions. It also provided a location for Unit 731, a place where Ishii would be able to conduct any experiment he deemed to be beneficial. Within his belief, animals could not supply useful data, hence using resources in the form of people plucked from the streets and locked in black vans known as voronki (ravens), to be carried off to the perverse unit in Harbin, China (Barrett, 2018). 

Japanese medical institutions sent top physicians and scientists, who would otherwise be labelled as Hikokumin (traitors) should they have refused to take part, employees seeing their work as noble service to the Emperor; the killing of non-Japanese held little significance to them. Salaries were generous, and there was an unlimited supply of funds from the Japanese government. After an attempted escape by 40 prisoners, all of whom were captured and killed, the unit moved to Pingfang in 1936 with a prison housing 500 men, women and children for vivisection (Barrett, 2018). The primary objective was to create biological and chemical weapons, where surgeries came from the expectation that human tests would create better weapons. Vivisections fell into four categories, not limited to weapons development: intentional infection of diseases, training newly employed army surgeons, trials of non-standardised treatments and discovering the limits of human tolerance to pain and stress (Barrett, 2018). The extent to which this caused medical advancement was limited, inherently killing people just to see how they reacted to being killed, with efforts of perversion being at the whim of doctors within the unit, provided with unlimited funding to do so. 

The use of research in war and its impacts

In 1938 and 1939, the Soviet and Japanese Armies clashed in two encounters near the border of Mongolia and Manchuria. The 1939 summer battle, known as the Nomonhan Incident and the Battle of Kalhin Gol by the Soviets, resulted in the consequent defeat of the Japanese Kwantung Army by Stalin’s Red Army. 

The first field operation of the biological warfare unit was in a desert region where water was scarce, therefore, the Japanese attempted to disable their Russian foes by dumping large quantities of intestinal typhoid bacteria into the river. Yet, the bacteria were ineffective once they hit the water, and was most likely a publicity stunt of Ishii’s as he would have known it would not have worked. Subsequently, in 1940, the Japanese dropped planes carrying wheat, corn, rags and cotton infected with the bubonic plague onto Ningbo, China, over 100 people dying within a few days of the attack as the village was unarmed (Barrett, 2018). 

Two years later, a second attack occurred in the same area, with researchers taking over a house on top of a hill a kilometre away from the infected zone to use as a vivisection laboratory, leaving Ningbo sealed off until the 1960s. After a series of failed biological attacks, either due to a lack of transportation to receive materiel, battles ending before usage, opposition by Japanese cabinet members, or even a vast suicide mission by submarine crews who carried such weapons, the Japanese considered a final use of biological weapons. The final use involved staging suicide germ attacks against occupying U.S. troops in Japan; however, it never took place once again due to opposition from the cabinet, which did not want Ishii to die in a suicide attack.

The resolution of World War II led to the commencement of the Cold War between the United States and the Soviet Union. Given the circumstances, Lieutenant Colonel Murray Sanders of the United States Army recommended to General Douglas MacArthur and President Harry Truman during the fall of 1945 that Ishii and his subordinates be given immunity from prosecution as war criminals. The reasoning was justified by Unit 731’s research value. MacArthur and Truman approved the deal, allowing Japan’s biological and chemical warfare development to remain a secret until the 1990s. 

A legal perspective on Unit 731’s ethical dilemma 

When examining the regulations of the time, these solely existed within the parameters of the Geneva Protocol of 1925. Yet, the protocol only prohibited the use of biological weapons, not their development, nor their production and acquisition, as a loophole. Established in 1864 by the Geneva Convention for the Amelioration of the Condition of the Wounded and Sick in Armed Forces in the Field, and later revised in 1906, 1929 and 1949, international humanitarian law exists to protect those who aren’t involved in fighting, such as civilians, medical and religious military personnel. It also serves to protect those who have ceased to take part, such as the wounded, shipwrecked, sick combatants or prisoners of war (ICRC, 2004). Ishii’s sadism inherent within his experimentation violated all five of the principles of International Humanitarian Law: humanity, distinction, military necessity, proportionality and limitation (Sanjaya, 2023). 

Firstly, humanity, namely the protection of human dignity and rights, irrespective of discrimination. Ishii’s inhumane treatment of vivisection without anaesthesia to study the operation of living systems on thousands of human beings (PAE, n.d.) violated the aforementioned principle. 

Secondly, the principle of distinction, to differentiate or distinguish between civilians and combatants as well as civilian objects and military targets, parties must solely direct such operations to military targets. The principle was violated, for example, by the invention of a germ bomb, made from fleas infected with the plague and flies smeared with cholera (Sanjaya, 2023), being indiscriminate with its victims when used. Moreover, the experimentation on civilians, such as Chinese elderly farmers and children, can be attributed to a lack of distinction. 

Next, the principle of military necessity stipulates a focus on military needs precisely suited to achieving the desired goal, with the military only using the appropriate methods, including weapons, to select targets that pose the least risk to people’s lives and civilian objects. Violation can be found in examples of frostbite testing by physiologist Yoshimura Hisato, where victims were routinely submerged in a tub of water filled with ice until they were frozen and a coat of ice formed over the skin (PAE, n.d.). Such tests were timed to check how long it would take to develop such frostbites and then had different methods to rapidly thaw the frozen appendage such as dousing in hot water, placing the limbs over open fire, or leaving the subject untreated overnight to see how long it would take for blood to thaw it out. 

The principle of proportionality can be ascribed to not causing civilian casualties and excessive damage, with levels of cruelty and risk disproportionate to purported research objectives. Using the frostbite example, Unit 731 proved scientifically that the best treatment for frostbite was to immerse it in water warmer than 100 degrees but never more than 122 degrees (PAE, n.d.). The methodology used to achieve such medical advancement as a research objective can be questioned on its moral and inhumane basis, disproportionate to the research benefits. 

Finally, the principle of limitation is to minimise unnecessary losses and casualties. Unit 731’s violation of ethical boundaries and its infinite number of victims, as well as the cause of an epidemic spreading even ten years later after a biological bomb (Sanjaya, 2023), shows its violation of limitations and the inherent value of minimising damage and casualties. 

In spite of these violations, Unit 731 researchers were not prosecuted, particularly Ishii, due to the Allies, in particular the United States, granting amnesty to Unit 731 in exchange for medical information and experiments. The aforementioned established a need for stricter international law to regulate biological weapon development, not just use, as stipulated by the 1925 Geneva Protocol. 

In 1972, due to regulatory necessity, the discussion of the issue began through the Biological and Toxin Weapons Convention (BWC), negotiated in Geneva during the Conference of the Committee of Disarmament to supplement the 1925 Geneva Protocol (UNODA, n.d.). In 1975, 184 countries signed the convention, agreeing not to develop, stockpile, obtain or store microbes or other biological agents, toxins, weapons or delivery devices related to biological weapons. The convention is reviewed on a regular basis, most recently from November 28 to December 16, 2022 (Sanjaya, 2023). 

Conclusively, we go back to our original question, weighing methodology and contribution to the betterment of humanity. A dilemma exists regarding whether it is worth granting amnesty to those who have contributed to science but have clearly violated statutes of international law to pursue such scientific advancement, which exists as precedent to protect ethics within medical research. If these are violated and justified by international actors, can we consider them to hold integrity to ensure they don’t happen again, thus needing consistent revision on the parameters of experimentation? Looking at the results of the Nanking Massacre, it is clear that the only reason for immunity from prosecution was for medical advancement. The ambiguous proportionality of future benefit from medicine and current exploitation of humanity to achieve it in some methodologies can subsequently be labelled as a worthy question of debate, concentrated within the point in history now concisely named Unit 731. 

*The name Maruta originates from locals questioning Unit 731’s substantial construction in Pingfang, which was answered by it being, namely, a “lumbar mill”. Thereon, the people were labelled as “logs”, relegating the prisoners to maruta (Barrett, 2018).