Operation Sea-Spray was a 1950 U.S. Navy secret Biological warfare experiment in which Serratia marcescens and Bacillus globigii bacteria were sprayed over the San Francisco Bay Area in California, in order to determine how vulnerable a city like San Francisco may be to a bioweapon attack.
From September 20 to 27, 1950, the U.S. Navy released the two types of bacteria from a ship off the shore of San Francisco, believing them to be harmless to humans. Based on results from monitoring equipment at 43 locations around the city, the Army determined that San Francisco had received enough of a dose for nearly all of the city's 800,000 residents to inhale at least 5,000 of the particles.
On October 11, 1950, eleven residents checked into Stanford Hospital for very rare, serious urinary tract infections. Although ten residents recovered, one patient, Edward J. Nevin, died three weeks later. None of the other hospitals in the city reported similar spikes in cases, and all 11 victims had urinary-tract infections following medical procedures, suggesting that the source of their infections lay inside the hospital. Cases of pneumonia in San Francisco also increased after Serratia marcescens was released, though a causal relation has not been conclusively established. The bacterium was also combined with phenol and an anthrax simulant and sprayed across south Dorset by US and UK military scientists as part of the DICE trials that ran from 1971 to 1975.