The Ningbo plague attack () was a secret biological warfare attack launched by Japan in October 1940 against the Kaiming Street area of Ningbo, Zhejiang, China, using fleas infested with plague (Yersinia pestis). A joint operation of the Imperial Japanese Army's Unit 731 and Unit Ei 1644, the attack was carried out by military planes taking off from Jianqiao Airport in Hangzhou, which airdropped wheat, corn, cotton scraps, and sand infected with plague fleas to target locations. From September 1940, Ningbo, Quzhou, and other places were subjected to various forms of biological warfare until the end of October 1940, when the attacks triggered a plague epidemic in Ningbo.
After the outbreak of the plague, the city authorities in Ningbo built an isolation wall high around the epidemic area, segregating patients and suspected cases, and eventually burned down the Kaiming Street area to eradicate the disease. Until the 1960s, this burned area was still referred to as the "plague field". According to the doctoral thesis of Junichi Kaneko, a military doctor of Unit 731, on October 27, 1940, Unit 731 spread of plague bacteria over Ningbo using aircraft, resulting in a total of 1,554 deaths from the first- and second-round infections.
Background Japanese biological warfare plan In June 1925, Japan signed the Geneva Protocol, which committed Japan to refrain from using biological and chemical weapons in warfare. The development of Japan's biological weapons was thus highly secretive and led by Shiro Ishii. He planned and raised funds for Japan's biological weapons program. In 1939, the Imperial Japanese Army established Unit Ei 1644 in Nanjing to conduct research on biological and chemical weapons. Units Ei 1644 and 731 studied the effects of various chemicals and pathogens that could be used as biological weapons on soldiers and civilians and developed weapons to further expand the Japanese Empire's territory in Asia.
After the failure of the rapid decisive victory plan in the war against China, the Japanese military began using bacteriological weapons. In the summer of 1939, during the Battle of Khalkhin Gol, the Imperial Japanese Army used biological and chemical weapons against Soviet and Mongolian troops. On June 13, large quantities of white powder were airdropped in the vicinity of Lihai, Shaoxing. On June 15, chemical tests conducted by the local river police did not reveal any abnormalities, but subsequent bacterial culture tests revealed turbidity in one test tube and cotton-like floating substances in another, with pathogens such as tetanus and diphtheria observed under a microscope. Within days after the airdrop, the weather in Shaoxing was clear and sunny, with abundant sunlight, which was not conducive to bacterial growth, so no epidemic outbreak occurred. This is the earliest recorded instance of the Japanese military's bacteriological weapon attack in Zhejiang.
Strategic location of Ningbo Before 1937, Zhejiang cities such as Ningbo, Jinhua, and Quzhou in Zhejiang did not experience a plague epidemic. However, people may have been aware of the plague near Ningbo in Shanghai in 1910. The incubation period of the plague is two to eight days. At the time of the outbreak, sulfa drugs, streptomycin, and other antibiotics had not yet been invented, so residents of Ningbo could not have access to antibiotics and were primarily treated with serum. Without treatment, the mortality rate of the plague was almost 100%, and there was not enough serum supply prepared in advance.
After the outbreak of the Second Sino-Japanese War in 1937, Ningbo became one of the important seaports for China to obtain international aid supplies, with a daily throughput of over 10,000 tons of goods. As a port city with a population of 260,000, Ningbo had numerous streets, dense housing, crowded residents, relatively poor sanitary conditions, high population mobility, and frequent goods entering and leaving, making it easy for the plague to spread and proliferate through people and goods transmission. Kaiming Street is a north-south urban main road in Ningbo and is the main commercial centre of the old city.
Since the first Japanese air raid on Lishe Airport on August 16, 1937, the Japanese military had directly attacked Ningbo at least seven times. On 17 July 1940, the Japanese military first invaded Zhenhai, but were driven out by the Chinese army five days later on the 22nd. The Japanese military again bombed Ningbo on 5 and 10 September of the same year.
Operation Decision-making
In June 1940, the Imperial Japanese Army headquarters formally discussed the use of biological weapons and issued orders to begin biological warfare. On 5 June 1940, discussions on the implementation of bacteriological warfare were held by Colonel Kozo Aramaki from the Operations Department of the Imperial Japanese Army General Staff, Major Kumaomi Imoto from the China Expeditionary Army Staff, and Lieutenant Colonel Tomosada Masuda, acting commander of Unit Ei 1644 in Nanjing. It was decided during the discussions that the main cities in Zhejiang would be targeted, and the method of operation would involve dispersing bacterial liquids from aircraft and air-dropping fleas infected with plague. On August 6, a heavily guarded train departed from the barracks of Unit 731 in Pingfang, bound for Hangzhou. The train was loaded with 700 aerial bombs, 20 vehicles, 70 kilograms of Salmonella typhi, 50 kilograms of Vibrio cholerae, and 5 kilograms of plague fleas. Shiro Ishii was the overall director of this operation.
On September 10, 1940, discussions were held in Hangzhou between the Central China Expeditionary Army and the Nara Unit, responsible for bacteriological warfare and composed of personnel from Unit 731 and Unit Ei 1644, to select the targets for the attacks: Ningbo and Quzhou, with Jinhua as a backup, to coincide with the blockade of the Ningbo Port by the Imperial Japanese Navy which commenced in July 1940. The Japanese army also referred to this operation as "Operation Hangzhou". According to the plan, aircraft would take off from Hangzhou Jianqiao Airport and drop ceramic bacteriological bombs developed by Shirō Ishii himself, along with cotton, shredded cloth, and other materials to protect the fleas. Corn and cloth were infested with fleas carrying pathogens of cholera and plague to infect rats, which would then transmit the diseases to human hosts.
Air raids During the three-month-long bacteriological warfare, six areas including Ningbo were subjected to various forms of bacteriological attacks. In Quzhou, the Japanese employed aircraft to scatter grain and wheat seeds carrying bacteria; in Ningbo, aircraft were used to spread bacteria-laden grains and cotton within or around the city; in Jinhua, explosions from bombs dropped by aircraft produced a pale yellow smoke; in Yushan, a plan was implemented to release bacteria among ordinary residents, with pathogens being introduced into pools and wells, and even by placing hundreds of seemingly abandoned desserts and fruits injected with large quantities of typhoid and paratyphoid bacteria by the Imperial Japanese Army at doorsteps and beside trees, deceiving local residents who lacked food to consume.
On 4 October 1940, wheat and barley items dropped by Japanese aircraft were found in Quzhou. That afternoon, the county magistrate ordered the residents of Quzhou to gather and burn the air-dropped items. Starting from 10 October, the area began to see deaths from the diseases. From 18 September to 8 October, the Japanese launched a total of six attacks on Ningbo, none of which resulted in a plague outbreak. Despite fleas being dropped in Quzhou on 4 October, there were no apparent effects by the end of October.On 22 October, Japanese military aircraft flew over Ningbo and dropped wheat and other items. The airstrikes in Quzhou did not attract the attention of the provincial government, which instead focused on a plague outbreak in Qiyuan, not associated with the Imperial Japanese Army.
At around 7 a.m. on 27 October, air raid sirens sounded in downtown Ningbo, and Japanese military aircraft flew over the streets of the city, dropping leaflets instead of bombs. According to eyewitness Hu Xianzhong, the leaflets depicted flags of Japan, Germany, and Italy, and a cartoon depicting "Sino-Japanese friendship", claiming that Chongqing was suffering from famine and hardship while the Japanese people were well-fed and had surplus food to help them. Around 2 p.m., Japanese aircraft reappeared and air-dropped barley, millet, flour, and clusters of cotton balls. Archibald Crouch, an American missionary in Ningbo, noted in his diary that while Japanese aircraft usually flew in groups when arriving in Ningbo, this time there was only one aircraft, which was unusual, and observed that after the aircraft passed, it seemed to release a cloud that dispersed downward. Local residents had no experience with plague outbreak, and no one mentioned that this was a biological weapons attack that day.
Epidemic Early spread
In 1940, Ningbo had yet to have piped water, so it was common for households to collect rainwater in one or two large containers placed under the eaves of their courtyards for drinking and cooking. On the evening of 27 October, heavy rain in Ningbo washed wheat grains from rooftops into these water jars. Some poultry that consumed the wheat grains died the following day. People noticed a sudden increase in fleas in Donghou Street and Kaiming Street, but there were no reports of mass deaths in rodents. Rumours circulated that the Japanese air raid was actually a biological weapons attack.
On 30 October, according to the local Chinese-language newspaper Shishi Gongbao, an acute disease outbreak was reported in Kaiming Street of Ningbo, spreading severely. Within just three days, over 10 deaths were reported. Subsequently, people from neighbouring establishments such as Wang Shunxing's bakery, Hu Yuanxing's dominoes shop, Yuan Tai Hotel, Bao Changxiang underwear shop on East Zhongshan Road, and the vicinity of Donghou Street, all experienced fatalities. Infected individuals exhibited symptoms including high fever, headache, dizziness, staggering gait, occasional confusion, swelling, and pain in the lymph nodes, and diarrhoea before death. Initially, people mistook it for bubos or malignant malaria. People sought quinine from hospitals, but it proved ineffective. On the morning of 1 November, nearly ten households in Kaiming Street, East Main Road, Donghou Street, and Taiping Alley reported deaths, with an increasing number suffering from colds and fever. Nine people succumbed to the disease on that day alone.
Immediate responses
On 1 November, the government of Yin County invited physicians to form a prevention and control committee, with Zhang Fangqing, the director of the Central Hospital, appointed as the head of the Medical Affairs Department, and Sun Jinshi as the attending physician. Based on Sun Jinshi's preliminary diagnosis of patient symptoms, they suspected plague, with the majority of patients suffering from septicemic plague, and a minority from bubonic plague, with no cases of pneumonic plague detected. Ding Licheng, the director of Hwa Mei Hospital, stated that it was still uncertain whether it was a genuine plague.
On the evening of 2 November, the county government imposed a blockade and isolation on the area and conducted routine disinfection of households. As a preventive measure, bed sheets and cloth were burned, and officials promptly began vaccinations.