Operation PX

Operation PX, also known as Operation Cherry Blossoms at Night, was a planned Japanese military attack on civilians in the United States using biological weapons, devised during World War II. The proposal was for Imperial Japanese Navy submarines to launch seaplanes that would deliver weaponized bubonic plague, developed by Unit 731 of the Imperial Japanese Army, to the West Coast of the United States. The operation was abandoned shortly after its planning was finalized in March 1945 due to the strong opposition of General Yoshijirō Umezu, Chief of the Army General Staff.