The Secret Japanese Plan for Biological Warfare

As World War II edged toward its conclusion, Japan grew increasingly desperate to turn the tide of the conflict. Among their final, sinister strategies was Operation Cherry Blossoms at Night, a biological warfare plan that, if executed, could have unleashed catastrophic destruction on the West Coast of the United States.

The mastermind behind this chilling strategy was Shiro Ishii, head of the infamous Unit 731—a covert program specializing in non-conventional weapons. Japan’s military, already crippled by successive defeats, recognized that conventional tactics could no longer reverse their fortunes. Ishii’s plan aimed to exploit biological warfare as a last-ditch effort to inflict maximum harm on their adversaries.

Southern California was chosen as the target for Operation Cherry Blossoms at Night. The weapon? Plague-infected fleas, designed to spread the deadly bubonic plague across densely populated areas. These fleas, meticulously engineered by Unit 731, would be delivered by kamikaze pilots using Aichi M6A Seiran aircraft launched from I-400-class long-range submarines.

This was not Japan’s first foray into biological warfare. The Imperial Japanese Army had previously unleashed germ warfare on occupied China, leading to devastating death tolls ranging from tens of thousands to as many as 400,000. Unit 731, under Ishii’s leadership, conducted grotesque experiments on human subjects, refining their biological weapons for maximum lethality.

Earlier in the war, biological attacks were considered during critical battles like Bataan in 1942 and Iwo Jima, but logistical and tactical challenges prevented their deployment. Operation Cherry Blossoms at Night, however, was dangerously close to being implemented.

On March 26, 1945, the plan for Operation Cherry Blossoms at Night was finalized. Five I-400-class submarines, each equipped with aircraft capable of carrying the infected fleas, were to launch a covert attack. Pilots would either drop balloon bombs loaded with plague fleas or deliberately crash their planes to disperse the infection.

This mission was designed as a one-way trip, with pilots and submariners fully aware they would not return. Ishio Kobata, one of Ishii’s pilots, later recounted how Ishii had bluntly described the suicidal nature of the operation.

The attack was scheduled for September 22, 1945. However, Yoshijiro Umezu, Chief of the Army General Staff, vetoed the plan, recognizing its moral and practical implications. Just weeks before the planned attack, the war took a decisive turn when Japan announced its surrender on August 15, 1945, following the atomic bombings of Hiroshima and Nagasaki.

The surrender rendered Operation Cherry Blossoms at Night moot, sparing the United States from a potentially devastating biological attack.

Although Operation Cherry Blossoms at Night was never executed, the mere existence of such a plan highlights the extremes to which desperate nations can go during wartime. Shiro Ishii and Unit 731’s atrocities left a dark stain on history, reminding us of the potential horrors of biological warfare.

Operation Cherry Blossoms at Night remains one of the most haunting “what ifs” of World War II. Its near-execution underscores the importance of vigilance and ethical considerations in warfare. While the surrender of Japan brought an end to these horrifying plans, the story serves as a sobering reminder of the lengths to which nations may go when facing defeat.

This chilling episode in history is a testament to the resilience of the human spirit in overcoming adversity and a cautionary tale about the devastating potential of biological weapons.