Operation Sea Spray

Operation Sea Spray was a classified U.S. Navy biological warfare experiment conducted in September 1950 over San Francisco Bay. The operation involved releasing approximately two million bacteria of the Serratia marcescens strain from a Navy minesweeper to study how biological agents would disperse over a populated urban area under real-world conditions.

The experiment was conducted without the knowledge or consent of San Francisco residents as part of a larger military program to understand the vulnerability of American cities to potential biological warfare attacks. Navy personnel used the minesweeper to create a bacterial cloud that drifted over the city for several days, covering approximately 117 square miles.

Serratia marcescens was chosen because military scientists believed it was harmless to humans, making it suitable for testing biological dispersal patterns over civilian populations. However, the bacterium is now known to cause serious infections, particularly in individuals with compromised immune systems or underlying health conditions.

Following the experiment, several Bay Area hospitals reported an unusual outbreak of Serratia infections, including eleven cases at Stanford University Hospital, one of which resulted in death. While the military initially denied any connection between the experiment and the outbreak, later investigations suggested a possible link, though causation was never definitively established.

Operation Sea Spray was revealed to the public in 1977 during congressional hearings on military biological experiments. The disclosure led to lawsuits against the government and contributed to stronger oversight of military experimentation involving civilian populations. The operation remains a significant example of unethical human experimentation conducted by U.S. military agencies during the Cold War period.