San Francisco.Justin Sullivan/Getty Images
On September 20, 1950, a US Navy ship just off the coast of San Francisco used a giant hose to spray a cloud of microbes into the air and into the city's famous fog. The military was testing how a biological weapon attack would affect the 800,000 residents of the city.
The people of San Francisco had no idea.
The Navy continued the tests for seven days, potentially causing at least one death. It was one of the first large-scale biological weapon trials that would be conducted under a "germ warfare testing program" that went on for 20 years, from 1949 to 1969. The goal "was to deter [the use of biological weapons] against the United States and its allies and to retaliate if deterrence failed," the government explained later. "Fundamental to the development of a deterrent strategy was the need for a thorough study and analysis of our vulnerability to overt and covert attack."