Query: What were the Japanese originally going to drop on San Diego from their kamikaze planes?
Context: During the final months of the war, the Japanese had a plan to target multiple U.S. cities for biological attack, starting with San Diego. The plan was called "Operation Cherry Blossoms at Night" and called for kamikaze planes filled with fleas infected with plague (Yersinia pestis) to crash into civilian population centers in the city, hoping to spread plague in the city and effectively kill tens of thousands of civilians. The plan was scheduled to launch on September 22, 1945, but was not carried out because Japan surrendered five weeks earlier.