• The use of disease as a weapon is nothing new. Centuries ago, armies would occasionally catapult the bodies of people who had died of plagues into cities under siege in hopes of spreading disease, a tactic that often proved successful. English colonists in the New World on occasion gave blankets and other items that had belonged to people who had died of smallpox to local native tribes, and the results could be devastating since the natives had little resistance to the disease.

These were purely opportunistic schemes. Methodical development of pathogens and potent biological toxins as weapons of mass destruction had to wait until the development of modern medical theory and the discovery of pathogens, in the last part of the 19th century.
Despite the fact that the knowledge to manufacture biological weapons or “bioweapons” was available in the First World War, there is no strong evidence that anyone did, although rumors of biological warfare (BW) were widespread at the time. The possibility of BW was certainly evident, and the Geneva Protocol of 1925 included clauses forbidding it. Development of bioweapons did not actually begin in earnest until the 1930s, with Japan taking the lead. The effort was directed by a single domineering figure, an Imperial Japanese Army officer and medical doctor named Shirou Ishii.
Ishii returned from a European tour in 1932, bringing with him a conviction that BW was the way of the future. Ironically, the fact that the Geneva Protocol had banned BW helped draw his attention to it, since the ban implied that people found such weapons unusually dangerous and frightening.
The Japanese invaded the Chinese province of Manchuria in 1932, and set it up as the Japanese puppet state of “Manchukuo”. In 1935, Ishii managed to convince his superiors of the potential usefulness of BW; they set him up in a hospital in Harbin, Manchuria, to conduct small-scale experiments with dangerous pathogens. By 1937, Ishii’s work had proved promising enough for the Japanese War Ministry to approve the construction of a full-scale BW research and development complex, at a small town named Pingfan, about 65 kilometers (40 miles) south of Harbin.
The Imperial Japanese Army had attacked China proper in that year. The Japanese were able to win almost every battle they fought, but they were completely outnumbered by the Chinese. The Japanese turned to BW as a potential equalizer. It is also possible that they hoped to exterminate Chinese in areas Japan intended to colonize.
The Pingfan Institute was completed in 1939. Ishii, now a general, was in charge of the research organization, which was given the cover designation “Water Purification Unit 731”. The Pingfan complex covered over three square kilometers (1.16 square miles) and included an airfield, barracks, and laboratories.
Japanese recruits arriving there found it an odd place. For example, none of the vehicles carried any identifying marks. They quickly found out that it had other strange and much more unpleasant features. One Japanese veteran who was a technician at the Pingfan site recalled there were many doctors and professors there, giving it something of the air of a university medical research facility, but noted that it was in fact the opposite: “Here, they were trying to find ways to kill people.”
There was a certain scientific challenge in this effort. The understanding of pathogens and their actions in causing disease and epidemics was crude, and there was, and is, still much to learn. There were also the practical problems of developing bioweapons, such as selecting the appropriate pathogen, determining the lethal dosage, and engineering the right techniques for production, storage, transport, and dispersal. Unit 731 also worked on defensive measures, primarily the large-scale production of vaccines.
Unit 731 studied almost every major known pathogen for its utility as a BW agent or “bioagent”. Some of the more significant included:
“Anthrax”, a highly lethal disease of livestock and humans. Anthrax is a bacterial infection that can be acquired by contact with infected victims, eating of tainted meat, or by inhalation of anthrax spores. When anthrax is acquired by contact, it can create hideous sores that may lead to death by blood poisoning, though the mortality is relatively low, no more than about 20%. The sores tend to be shiny black with dried blood, which gives the disease its name, since the word “anthracis” is Greek for “coal”. Mortality is about 50% if the bacteria are ingested by eating tainted meat, though this form of anthrax is very rare. However, when inhaled, it leads to a lung infection that is over 90% lethal, killing in a few days. The action of inhalation anthrax is dangerously deceptive, since the victim suffers an initial bout of what feels like the flu, which then seems to fade out. In fact, all that has happened is that the anthrax spores have been scavenged up by the body’s lymphatic system, where they then proceed to multiply, bringing on a second and murderous bout of the disease. The bacteria actually kill by secreting a deadly toxin that results in toxic shock. The purified toxin itself can in principle be used as a deadly bioagent.

The only good thing about anthrax is that it is not contagious as such, though since a victim’s corpse is full of spores, cremation is usually advisable. The lack of contagiousness is actually an advantage when using it for BW, since it helps ensure that only those directly attacked will come down with the disease. In fact, anthrax would become the lethal bioagent of choice for future BW development programs. Its spores are very hardy and easy to store for long periods of time, and can be conveniently packed into munitions. Anthrax spores are so hardy that they will persist in an area over which they have been spread for decades, though they are sensitive to bright sunlight.
“Plague”, the “Black Death” of Medieval times, is caused by infection from a bacterium named Yersinia Pestis. It has three forms: “bubonic plague”, when spread by fleas or other parasites; “pneumonic plague”, when spread by inhaling the bacteria; and “septicemic plague”, when spread by contact. Pneumonic plague has a lethality of 95% or more. Although bubonic plague is somewhat less lethal, its spreads more easily and is more useful for BW. However, bubonic plague still isn’t all that good a bioagent, since it requires the accumulation, storage, and distribution of live fleas.
“Gas gangrene”, a condition caused by the infection of wounds by the Clostridium perfringens bacterium, characterized by stinking putrefaction of the flesh.
“Brucellosis”, a bacterial disease caused by various pathogens of the genus Brucella that infects livestock and humans. It is not very lethal, but it is highly contagious and can incapacitate a victim for a week or more.
“Tularemia”, a bacterial disease caused by the bacterium Francisella tularensis that infects rabbits as well as humans, and so is known as “rabbit fever”. Like brucellosis, tularemia is rarely fatal in humans but can make a victim wretchedly sick for a time.
“Glanders”, a disease of horses and humans that eats away the mucous linings of nose and respiratory tract, and attacks the lymphatic system. It is caused by the bacterium Pseudomonas mallei. It is uncertain if the Japanese were interested in glanders for killing horses and mules, or humans, or most likely both.
Bacteria related to food poisoning, including the Salmonella and Clostridium botulinum bacteria, which secrete extremely deadly biotoxins. The toxins were potential bioagents in themselves, particularly botulism toxin. The lethal dose of botulism toxin is very small, and the toxin is easily produced in quantity and stored for long periods of time. Other pathogens investigated included typhus, typhoid, cholera, tetanus, smallpox, and tuberculosis, but these agents proved difficult to “weaponize”. The Japanese also experimented with exotic biotoxins, such as blowfish poison. They were traditionally familiar with this toxin, since blowfish is regarded as a delicacy in Japan but has to be prepared by a specially-qualified chef so that it may be eaten without fatal results. Incidentally, as with chemical agents and chemical weapons, a “bioagent” only refers to a pathogen or toxin itself, while a “bioweapon” is a delivery system loaded with bioagents.

  • The Japanese had to produce pathogens in quantity for tests and, if they proved worthy, production. Unit 731 researchers devised a scheme using trays of meat and broth as cultures. The trays were kept in incubators and the scum of bacteria produced was skimmed off every few days. The stink of rotten meat was almost overpowering. Eventually, Pingfan was believed to have been capable of producing tonnes of pathogens every month.

Having obtained pathogens, the next step was to determine their effectiveness. There were plenty of Chinese available for use as involuntary test subjects. The Japanese would put up posters warning the Chinese that epidemics of the appropriate diseases had broken out, and then a squad of soldiers would go out and dump pathogens discreetly into the well of a village. Three or four days later, they would return to inspect the ill. The soldiers would anesthetize them, cut them open and take samples, and sew them back up again. “Then we threw the bodies down the well,” as a veteran of the program recalled. The soldiers torched the village and left.

The tests were very successful. General Ishii then decided to perform more controlled tests in deep secrecy on Chinese prisoners taken to the compound at Pingfan. Many of these people were simply rounded up off the streets of Harbin to meet quotas set by Unit 731 officers. At least 3,000 were taken there, and few, if any, ever came back. Another cover story for the compound was that it was a lumberyard, and so Unit 731 personnel referred to the prisoners as “maruta (logs)”. Prisoners were assigned serial numbers 1 through 200. Once that block had all been killed, the serial number count started over again through the next 200, and so on. Japanese veterans of Unit 731 recollect the place as a kind of hell on Earth, but the Imperial Japanese Army demanded unhesitating obedience. Soldiers were routinely struck by their NCOs, and insubordination of any sort was unthinkable, meriting immediate and severe punishment.
Chinese prisoners were tied to poles out in the open and forced to look into the sky as airplanes flew over and sprayed bacteria on them. The prisoners were carefully observed and their condition recorded with colored drawings as they sickened and died. Others were tied to stakes or panels and arranged around fragmentation bombs containing Clostridium perfringens bacteria. The bomb was detonated, and the test subjects were studied as they developed gas gangrene from their wounds. When test subjects died, their corpses were burned in a crematorium.

  • By 1940, Unit 731 had developed a ceramic anthrax bomb and built 4,000 of them. They were also considering ways of delivering bubonic plague. Researchers at Pingfan bred plague-infested rats in quantity and then gathered the fleas from the rats. The fleas could then be distributed as a bioagent vector, using tubular baskets strapped to the bomb pylons of aircraft.

In October 1940, a Japanese aircraft flew low over the city of Ningpo, which was still held by the Nationalist Chinese, and dispersed a spray containing plague-infested fleas. The results were appalling. Roughly 500 people died and the city was panic-stricken. One survivor recalled: “There were so many people and not enough coffins. So two people would share a coffin.” It is thought that more attacks may have taken place in China, but records of such activities were destroyed by the Japanese at the end of the war and nobody knows for sure.

The researchers at Unit 731 went on to even more imaginative BW studies. They decided to use Chinese prisoners not merely to test pathogens, but to actually act as production incubators to breed them. The researchers believed that pathogens that managed to overcome the body’s defenses were likely more virulent. The prisoners were injected with pathogens. When the victims reached their limit, the prisoners were chloroformed and all the blood was drained from their bodies. When the blood flow from a prisoner slowed down, a soldier would jump on the man’s chest to force out the last drops. One Japanese veteran recollected: “They did not leave even one drop of blood in the body!”

With such extensive handling of pathogens there were likely to be accidents, and it is believed that hundreds of Japanese staff of Unit 731 died from the pathogens they handled. Despite this problem, Ishii’s BW research empire spread, establishing 18 satellite stations in China and in other locations ranging from Hokkaido to the Dutch East Indies.

The Japanese BW researchers not only investigated pathogens to attack people, they also studied chemical herbicides and pathogens to destroy crops. The most intensively studied plant pathogens were “fungal smuts” and “nematode worms” intended to attack Soviet and North American wheat fields. Smuts in particular were potentially highly effective bioagents. The head of a wheat plant infected by wheat smut turns into a blackened mass of spores that are released into the air to infect other wheat plants downwind. The Japanese developed a production facility that could yield about 90 kilograms (200 pounds) of smuts annually.