As World War II started to draw to its inevitable conclusion, the Japanese became increasingly desperate. Japan, which had had been suffering crippling defeats, wasn’t about to go down without causing as much damage to their enemies as they could. That included making plans for a biological warfare attack that would have devastated the west coast of the United States.

The plan was devised by Shiro Ishii, who gave it the code name Operation Cherry Blossoms at Night. The United States had proven by its response to Pearl Harbor that a conventional attack—no matter how devastating—wouldn’t keep them from preventing Japan regaining the upper hand in the Pacific. Too much damage had already been done to the Japanese forces, and the Allies had advanced too far west across the Pacific.

Ishii devised a plan that would have used a pathogen created by the infamous Unit 731, a secret operation devoted to research and development of non-conventional weapons. The target of Operation Cherry Blossoms at Night was Southern California. The specialized researchers at Unit 731, known for their grotesque experimentation on human subjects, had weaponized bubonic plague, which would be dispersed by infected fleas.

Prior Use of Biological Warfare by Japan

It wouldn’t be the first time biological warfare would be used by the Japanese. The estimated death toll from germ warfare orchestrated by the Imperial Japanese Army in occupied China ranged from the tens of thousands to 400,000. But it would be the first time such weapons were used against the United States.

Biological attacks had previously been considered against American troops, first during the Battle of Bataan in March of 1942, and later at the Battle of Iwo Jima.

Operation Cherry Blossoms at Night

Operation Cherry Blossoms at Night came dangerously close to becoming reality, with the plan finalized on March 26, 1945. Aichi M6A Seiran aircraft carrying plague-infected fleas would launch from five I-400-class long-range submarines. According to the plan, the planes would either drop the plague in balloon bombs or purposely crash in order to disperse the infection. The mission was considered to be a suicidal attempt at hitting a major population center, and pilots and submariners were not expected to return. A pilot serving under Ishii, Ishio Kobata, recalled the plan, stating that Ishii had approached him and was direct about the kamikaze nature of the attack.

A Narrow Escape

The attack was scheduled to be carried out on September 22, 1945, but Yoshijiro Umezu, the Chief of the Army General Staff, vetoed it. Of course, the entire plan became moot on August 15, 1945, when the Japanese surrendered, ending the War in the Pacific.