In August 1944, General Otozo Yamada, commander of Japan's Kwantung Army, toured Unit 731, the secret biological weapons centre in Japanese-occupied Manchuria, where storehouses bred vast numbers of fleas meant to spread plague among enemy soldiers dropped from aircraft. Within a year the Kwantung Army was crushed by Soviet forces and Yamada was captured. Under interrogation, he admitted Unit 731 had been built to wage biological war against the Soviet Union, Mongolia and China.
Border clashes and a neutrality pact
In the late 1930s the Soviet Union and Japan fought bloody clashes near Lake Khasan and later at Khalkhin Gol in Mongolia, both won by the Red Army and its Mongolian allies. On April 13, 1941, the two countries signed a neutrality pact in Moscow. Despite pressure from Adolf Hitler, Japan, shaken by Soviet strength at Khalkhin Gol, never declared war on the USSR.
Tokyo nonetheless wanted Soviet territory as part of its planned Greater East Asia Co-Prosperity Sphere. Japanese planners had drawn up schemes to install a military administration in the Far East after any occupation, scrap Soviet laws and strip residents of political rights. Secret Japanese documents referred to the USSR as "Object No. 1" and treated war as inevitable. Geographer Yamamoto Kumataro wrote in 1942 that Siberia's forests made it natural for the region to share Asia's fate.
Shiro Ishii and the birth of Unit 731
The driving force behind Japan's biological warfare programme was Shiro Ishii, a microbiologist and lieutenant general whose fixation on bacteria had unsettled fellow students at university. He won military backing after a two-year tour of the West studying the effects of chemical weapons used in the First World War, then built a bacteriological laboratory within the Kwantung Army after Japan seized Manchuria.
For cover, the programme was first named the Kwantung Army Water Supply and Epidemic Prevention Department, with a second branch called the Epizootic Prevention Department. After Nazi Germany invaded the USSR in 1941, these were recoded as Unit 731 and Unit 100; a third, Unit 1644, was also formed. All three were staffed with leading Japanese microbiologists and heavily funded. By summer 1941 Japan's chief of general staff was demanding faster plague research and mass breeding of infected fleas. Major General Kiyoshi Kawashima, who headed the unit's production department, later said Manchuria was meant as a staging ground for war on the USSR.
Inside Unit 731 at Pingfan
From 1940 Unit 731 operated from Pingfan station, about 30 kilometres from Harbin in the Japanese puppet state of Manchukuo, a guarded compound whose staff wore uniforms stripped of rank insignia. It produced plague, typhoid, paratyphoid, dysentery and cholera bacteria, and ran four branches along the Soviet border, at Hailin, Linkou, Sunwu and Hailar, whose staff signed pledges of secrecy that extended to their own families.
Command ran through the Kwantung Army's commander, first General Yoshijiro Umezu and, from 1944, Yamada; only they could order germ weapons used against enemy troops. Yamada later described the methods himself: bacteria dropped from aircraft in special bombs or sprayed from onboard devices, or spread on the ground by contaminating water, pasture and livestock. Test bombs were dropped on ranges where Chinese or Manchurian prisoners, tied to posts so they could not flee, were used as targets.
Ryuji Kajitsuka, who had headed the war ministry's medical sanitary department from 1934 to 1937, helped install Ishii as the unit's chief and oversaw its bacteria research and study of disease-carrying insects. At the 1949 Khabarovsk trial he admitted knowing the experiments were conducted on living people, and said the programme was aimed chiefly at the USSR, Mongolia and China, as well as Britain and the United States. Seoei Yamamoto, who worked in the unit's paratyphoid and tuberculosis laboratory, said he had two microscopes, a centrifuge, an autoclave and glass tubes at his disposal, and was tasked with finding ways to preserve and strengthen the bacteria's virulence.
Human experiments in the prison camp
Unit 731 kept its own prison. Up to 600 Manchurian and Chinese prisoners sentenced to death by Manchukuo authorities were delivered there each year, alongside Soviet civilians abducted from border settlements, captured border guards and sailors from Lend-Lease ships sunk by Japan. Kawashima said he personally saw the condemned brought in whole batches.
Two barracks held up to 200 prisoners each, with up to four to a cell, lit by four floodlights and guarded around the clock. Food was kept plentiful to keep subjects healthy enough for testing, and the buildings included operating rooms and X-ray facilities.
Separate cells were set aside for each disease, Kawashima said, and prisoners infected in the laboratories were moved to the matching cell. Cells held nothing but sleeping mats, and prisoners were led out in handcuffs under guard by trusted veteran soldiers personally selected by Ishii's brother.
From 1942, Soviet prisoners from the Hogoin camp near Harbin were sent to the unit to be killed, taken up to 20 at a time in covered trucks and tested with bacteria and poison gas. Private Demchenko was sent to his death after refusing under torture to give information about the USSR; officer Ignatov followed for anti-Japanese agitation among fellow prisoners; and Kanev, Pereboev and Romanchenko were sent for experiments after trying to escape Hogoin. Uniforms stripped from captured Red Army soldiers were reused by the Japanese for sabotage operations inside Soviet territory.
At the end of 1943, ten prisoners were tied to posts five metres apart and a fragmentation bomb was detonated 50 metres away; in spring 1944 a similar test used plague bacteria on another ten. Unit officer Nishi Toshihide testified that in January 1945 he took part in infecting ten Chinese prisoners of war with gas gangrene to test whether the disease could spread at minus 20 degrees Celsius. The men were tied to posts 10 to 20 metres from a gangrene-laced bomb, their heads and backs shielded with metal plates and padded blankets while their legs and buttocks were left exposed. All were wounded in the legs or buttocks and died in agony within seven days. In a separate test one prisoner's leg was deliberately frozen while the other was left untouched for comparison.
No one left the facility alive. Prisoners who survived infection were nursed back to health and fed only to be experimented on again, Kawashima said, until they finally died from disease. Bodies were burned in a crematorium on site. Over five years of operation at Pingfan, at least 3,000 people died there.
Attacks on Chinese territory
Japanese staff filmed the effects of plague on their victims. The weapons were never used in open battle against Soviet forces, though bacteria were used to contaminate river water at Khalkhin Gol during the 1939 fighting in Mongolia. In 1940 an unusual plague outbreak followed the aerial release of infected fleas near the city of Ningbo.
In summer 1941 Ishii sent 50 bacteriologists and technicians to scatter plague-infected fleas over the city of Changde near Dongting Lake, an important hub for Chinese military communications, triggering an outbreak there and in the surrounding area. In 1942 Unit 1644 contaminated Chinese territory being abandoned by retreating Japanese troops with plague, cholera, typhoid and paratyphoid bacteria, and poisoned wells and water bodies along the Zhejiang-Jiangxi railway. Yamada later said he personally did not consider the experiments a crime against humanity, since no international law explicitly banned them.
Unit 100 worked on a smaller scale, cultivating pathogens that caused disease in cattle and horses and testing ways to infect animals, including by spraying microbes from aircraft. Unit 1644 produced little vaccine but had substantial capacity for growing live bacteria. In spring 1945 Japan sharply increased the trapping and breeding of rodents and the cultivation of fleas for Unit 731, convinced that biological war was imminent within months.
Defeat, destroyed evidence and impunity
In August 1945 the Red Army, together with Mongolian forces, destroyed the Kwantung Army in Manchuria. On August 11 and 12, staff at Unit 731 hurriedly demolished its buildings, equipment, materials and documents, and personnel were issued poison ampoules to use if captured.
While preparing the Tokyo war crimes trial in 1946, American officials showed interest in Unit 731's leaders and asked Moscow to help interrogate Kwantung Army officers held in Soviet captivity. The United States later declined to bring cases involving biological weapons before the main tribunal. Ishii himself was arrested by American forces at the end of the war and granted immunity from prosecution in exchange for information about his experiments.
Soviet authorities wanted to try Ishii and asked General Douglas MacArthur, commander of the Allied occupation forces, to hand him over, but the request was refused. Some commanders directly tied to Unit 731 did face the Soviet military tribunal in Khabarovsk in 1949: Yamada, Kajitsuka, Kawashima and Unit 100 chief Takaatsu Takahashi were each sentenced to 25 years, with others receiving shorter terms. They were later held in a prisoner-of-war camp for generals near Ivanovo.
None served their full sentences. Yamada was amnestied, released early and repatriated to Japan in 1956. Ishii's trail after the war goes cold; he is thought to have lived quietly, either in Japan or in the United States.
