On September 18, 1931, elements of the Imperial Japanese Army (IJA) carried out an invasion of the north-eastern Chinese region of Manchuria, an area long contested between China, Japan, and Russia for its economic potential and natural resources sector. Appeals by the Chinese government to the League of Nations failed to move the Japanese government, which was effectively side-lined by the radicals in the armed forces in the following months as the public was whipped up into an unprecedented patriotic fervour, and international pressure calling for Japan to withdraw would only result in its departure from the League of Nations. Manchuria subsequently became home to a puppet state known as Manchukuo, nominally ruled by Puyi, the last Emperor of China, but in practice governed by Japanese officers and bureaucrats.
It was in this period and region that Ishii Shiro would emerge to put his ideas for biological warfare into practice. Ishii was a senior army surgeon and medical researcher who had a keen interest in bacteriology, to the extent that he had a fondness for raising bacteria as companions or pets. Characterised as childish and psychopathic, Ishii was nonetheless convincing and well-liked, overcoming the intense factional rivalries of the Japanese military to earn the patronage of officers in the rival factions of the interwar IJA, in a period where junior officers from both were assassinating each other's superiors as well as government officials. For over a decade, Ishii had advocated Japan to begin developing biological weapons, and his campaigning paid off when, after the invasion of Manchuria, he was given funding and facilities to begin experimenting with germ warfare, with Unit 731 being founded in the Pingfang District near the city of Harbin, under the guise of the Epidemic Prevention and Water Purification Department.
The Epidemic Prevention and Water Purification Department was a subsidiary of the Kwantung Army, the IJA’s formation stationed in northeast China. Unit 731 was one of numerous other units which operated under the Department, with the other units stationed throughout Japanese-occupied China and Southeast Asia, but took primacy as the main section which directed its weapons research and deployment. The overall purpose of the Epidemic Prevention and Water Purification Department did follow its pretexts to some extent - Unit 731 and its affiliates conducted medical research in these fields, and employed some of the best and brightest of Japan’s medical talents. It even developed and demonstrated a mass-production water filter named for Ishii himself, which led to an incident in which Ishii demonstrated the filter for Emperor Showa, among other dignitaries, by urinating in the filter in front of the witnesses and then offering the contents which emerged to the Emperor himself.
This cover, however, cannot disguise or diminish the scope of Unit 731’s activities, which were first and foremost dedicated to biological weapons research. The list of diseases which Unit 731 bred and experimented with included cholera, typhus, botulism, trench foot, anthrax, and bubonic plague. The experiments with bubonic plague included a rat breeding program in order to raise plague-carrying fleas, as well as successive tests to create as potent a strain of plague as possible. To test their infectivity and mortality, Unit 731 interred thousands of people, ranging from prisoners of war to common criminals to civilians unlucky enough to be abducted by the Kempeitai at any given moment, and deliberately infected them with their diseases, then left them to die horrible deaths. These test subjects, dubbed maruta - logs in Japanese - as a form of dehumanisation, faced many other grisly experiments, such as outdoor “frostbite tests” in -40ºC weather, exposure to poison gas in sealed chambers, and live vivisections, and very few managed to survive.
All of this was sanctioned by the Japanese military establishment. Unit 731 had been founded with Emperor Showa’s assent, and in addition to the aforementioned support Ishii had earned from his Army superiors, he also enjoyed patronage from Prince Takeda Tsuneyoshi, chief treasurer of the Kwantung Army, and Prince Chichibu, the Emperor’s brother. That said, there were critics - the Emperor’s youngest brother, Prince Mikasa, eventually criticised the program as a result of his shift to opposing militarism and expansionism, and some civilian politicians were also hard to win support from. This led to another incident involving Ishii in which he threatened to break a jar he claimed to be full of cholera on the Minister of Finance’s desk when he was refused funding, and when this threat failed, later broke into the minister’s home.
So now we get to the question: did this pay off in the end? Did Ishii’s visions of a future war whose victory would be determined by biological warfare play out? As one can probably tell by the outcomes of the wars in China and the Pacific, no, but the answer starts a bit earlier than that. In 1939, tensions between Japan and the USSR rapidly escalated as troops on both sides engaged each other on the Khalkhin Gol, the eastern border between Soviet-aligned Mongolia and Manchuria. Ishii, as with most officers, expected a full-scale war to break out for Japan to finally fulfill its long-anticipated expansion into Siberia. However, the Kwantung Army’s position in the region was highly disadvantageous due to its pursuit of offensive combat against a numerically superior enemy in the Red Army, and, finally prompted by heavy losses that forced the Japanese to regroup, Unit 731 was mobilised for its first combat operation in June. Unit 731’s bacteriological agents were moved from the Pingfang facility to the frontlines near the Khalkhin Gol, and disease prevention measures such as the distribution of Ishii’s patented water filters were conducted along the frontlines.
The attack was conducted on July 12, 1939. A “suicide squad” was deployed to the Khalkha River and dumped a jellied bacterial solution consisting of cholera, typhus, and dysentery into the river, in the hopes that the contaminated water would infect Soviet water supplies and cause mass casualties among the Soviet troops. Although the attack was to be originally carried out with aerial deployments that would be seen in later attacks, Soviet air superiority over the Khalkhin Gol made doing so too dangerous for the delivery aircraft. It is not known how many Red Army soldiers were infected, and at the very least there would have been few to no casualties, stemming from the fact that contrary to Japanese belief, the Soviets sourced their water supplies from well behind the frontlines, and took many simple precautionary measures such as boiling their water to prevent diseases from spreading in the first place. What is known, however, is that despite the thorough decontamination measures given to the “suicide squad” after their mission, over 1,300 Japanese and Manchu soldiers were infected with dysentery which almost certainly came from the agents Unit 731 had deployed into the river. Of those, it is also not known how many of them ultimately succumbed, though infected Japanese soldiers were sent to the Home Islands to receive medical treatment from Unit 731-associated military medical units.
Despite this apparent failure, the actions of Unit 731 were hailed as a success, and Ishii and the “suicide squad” were decorated for their actions. As such, Unit 731’s pathogens would be deployed for use in China, as the initial Japanese advances were blunted by the Chinese resistance. Beginning in autumn 1940, weaponised plague would be used tactically, followed by strategic biological attacks from that October. Cities such as Quzhou, Ningbo, Changde, Wenzhou, and Taizhou would all be attacked with biological weapons through plague fleas contained in ceramic bombs designed to shatter on impact, resulting in thousands of civilian casualties and the effects of the plague lingering for decades after. Biological warfare reached its peak during the Zhejiang-Jiangxi Offensive in 1942, with large raids taking place against villages and towns in Zhejiang, Jiangxi, Hunan, and Yunnan. Unit 731 specialists attached to the ground forces infected wells, left germ-ridden foodstuffs, and even sprayed the ground to infect Chinese troops in areas where Japanese forces had fallen back. These attacks went well beyond the preceding ones, as in addition to using the same types of bacteria from previous attacks, new specimens were employed, namely anthrax and rotten foot disease.
While gratuitous in their nature, these attacks did possess tactical and strategic considerations. Quzhou, the site of the first biological attack against a major population centre, was home to the regional Chinese barracks and was heavily garrisoned. Changde, the second largest city in Hunan, was attacked concurrent with a Japanese offensive in Hunan to seize the provincial capital, Changsha, and was probably launched to isolate the city due to the immense losses the IJA had incurred taking it in the prior months. The town of Baoshan in Yunnan, near the border with Burma, was targeted to disrupt operations on the Burma Road. This did not apply universally, though. While Ningbo was a hotbed of anti-Japanese resistance, its attack appears to have been partly for demonstrative and research purposes, as its process and aftermath were documented by Ishii’s researchers, leading to further refinements in the germ bomb design. Film reels from this attack were also shown to high-ranking Japanese officials, including Prince Chichibu. Biological weapons deployments in the Zhejiang-Jiangxi Offensive appear to have been especially unwarranted, as the campaign was primarily conceived as a reprisal to the Doolittle Raid, especially since most of the American pilots who landed in China were rescued and sheltered in Zhejiang. Further putting the utility of biological warfare into question were inadvertent infections of Japanese personnel, with one source estimating as many as 10,000 infected and over 1,700 killed by the same diseases targeted at their enemy.
All of the above is more than enough speculative fuel for alternate history, but pales in comparison to their most ambitious project - a biological attack against the Western Allies. Early proposals were originally tactical in nature - during the Battle of Bataan in 1942, in which American and Filipino forces fought a desperate last stand against the Japanese invasion of the archipelago, it was proposed that over 200 pounds of plague fleas would be dropped on the defending forces in ten separate attack waves, but the surrender of the defenders precluded such a possibility. Later, as the tide of the war was firmly against Japan, biological weapons were brought forward as a defensive weapon. There was an attempt to carry plague fleas to the strategically vital island of Saipan in the Northern Marianas to use against the American landing there in 1944, but the ship carrying them was sunk by an American submarine. Similarly, a plan to bring plague-laden gliders to the Battle of Iwo Jima did not materialise after the gliders failed to appear at Pingfang’s airfield to pick up their deadly load.
Going beyond this scope, Unit 731 proposed targeting major population centres on the U.S. West Coast to disrupt the American war effort. The initial plans envisioned the use of balloon bombs, designed to be cheaply made from paper with little manual labour, which would be fitted with a payload and carried across the Pacific Ocean by easterly jetstream winds at high altitudes. These bombs were originally created to carry incendiary payloads in order to cause large forest fires in rural Washington, Oregon and California, but could just as easily be modified to carry Ishii’s bacterial bombs. However, launches from November 1944 to February 1945 with conventional explosive or incendiary ordnance failed to deliver adequate results, as very few of the nearly 10,000 bombs launched managed to reach North America, and those that did failed to cause any palpable damage. American wartime censorship which hushed up any details of the bombs also meant that Japanese intelligence failed to learn of any successes, and no bombs were ever launched with bacterial payloads once Japanese intelligence concluded that the balloon bomb campaign was a total failure.
A second proposal surfaced with the entry of the I-400 class aircraft-carrying submarines into service with the Imperial Japanese Navy (IJN) in 1944. The largest submarines built until the 1980s, these vessels were designed to stealthily carry three Seiran seaplane bombers each across the ocean to attack targets in North America. While normally armed with conventional ordnance to attack strategic assets like the Panama Canal, the aircraft and their objectives could just as easily be modified to carry germ bombs. This gave root to Operation Cherry Blossoms at Night, an operation devised by Vice-Admiral Ozawa Jisaburo, the final Commander-in-Chief of the IJN Combined Fleet and Japanese commander at the Battles of the Philippine Sea and Leyte Gulf, which would deploy a squadron of I-400 class submarines to positions just off the American West Coast, from which they would launch air raids using bacterial weapons against San Francisco, Los Angeles and San Diego. The mission was first proposed in December 1944 by the Navy in coordination with Ishii Shiro and Unit 731, and finalised on March 26, 1945. However, it was vetoed and shelved by the Chief of the IJA General Staff, General Umezu Yoshijiro, who stated that “If bacteriological warfare is conducted, it will grow from the dimension of war between Japan and America to an endless battle of humanity against bacteria. Japan will earn the derision of the world.”
One final plot to attack the Americans came in August 1945, shortly after Japan surrendered, in which Ishii proposed biological terrorist attacks against the American occupation authorities. Details about this proposal are sparse and fragmented, but a memorandum uncovered in 2006 shows that Ishii’s superiors, including General Umezu, told him and the germ research teams not to die in vain with such attacks.
Given that these attacks amounted to nothing more than proposals and operations that hardly got off the ground, there is no true way to determine whether these attacks would have been effective. Would a bubonic plague outbreak create a regional or nationwide epidemic that would fulfill Ishii’s lofty aims of bringing the United States to a standstill? How would the Allies respond if or when they traced the origins of the outbreak to a Japanese air raid? This of course warrants the considerations of the advantages of American infrastructure, and therefore its ability to respond and contain the outbreak. Some outbreaks in China, like in Ningbo, were contained relatively effectively by a prompt local response, as authorities quarantined the infected district and its citizens, containing residents until they were cleared of symptoms or died, and later burning down the district to destroy any traces of the plague, as well as embarking on an anti-rat campaign to stop the spread of plague fleas. Could such a response be replicated in Los Angeles? And what of Bataan or Saipan, or other major battles like Okinawa and Manila?
In the end, these questions will remain hypotheticals due to the war’s conclusion, but it is worth addressing the fate of Unit 731. When the Soviet Union invaded Manchuria in August 1945, Unit 731’s facilities and documents were destroyed in order to eliminate as much evidence as possible of their acts. Eventually, however, initial denials to investigators gave way to admissions of their guilt. On the orders of Douglas MacArthur, Unit 731’s activities were covered up by the United States military, with Ishii and other Unit 731 personnel granted immunity from trial, and their details withheld during the Tokyo Trials. The Soviets and Chinese, for their part, would conduct trials of Unit 731 staff, with the Khabarovsk trials in December 1949 seeing twelve Unit 731 personnel sentenced to up to twenty-five years in hard labour. However, all would be repatriated to Japan in 1956, suggesting that the Soviets, like the Americans, offered clemency in exchange for information on biological weapons research. These personnel, including Ishii, would reintegrate into civilian life; with many continuing medical practices as civilians - one notable member would be a co-founder of pharmaceutical company Green Cross.
The legacy of Unit 731 would be felt in both superpowers as well as in East Asia. On the American side, surviving Unit 731 research contributed to the establishment of an American biological weapons program at Fort Detrick, Maryland. Research into biological weapons would cease in 1969, but the germ research laboratories would not close until 2019. On the Soviet side, post-war biological weapons research was conducted under Lavrentiy Beria, the head of the Soviet secret police. During the Korean War, Communist China and North Korea would allege that the United States conducted biological warfare, using plague akin to Unit 731, however, these allegations are heavily challenged by evidence from Russian sources strongly suggesting the accusations to have been an anti-American disinformation campaign, and as such the veracity of these claims is still subject to heavy contention by historians. Years later, in 1979, anthrax was accidentally released in the Soviet city of Sverdlovsk from a bioweapons research facility, itself built based on research gathered from Unit 731, resulting in at least a hundred deaths according to official sources.
Meanwhile, Unit 731 itself continues to be scrutinised, especially in the highly charged nationalist environment of modern East Asia as China and both Koreas continue to press claims for apologies and compensation while the Japanese government denies or downplays its actions. Former personnel, for their part, have come forward admitting their involvement and apologising to victims and their kin, but as the legitimate grievances of victims have been co-opted to fuel nationalism and xenophobia on both sides, it seems that their hopes for a resolution may be just as distant as they were half a century ago.