In the early years of the Cold War, military and intelligence planners in the United States grew intensely concerned with the potential threat of covert biological warfare. At Camp Detrick in Maryland—the sprawling, highly classified nerve center of the military’s biological warfare research—scientists continuously studied ways to turn germs into weapons of war and to defend against similar foreign operations. To understand how pathogens might disperse and behave when released over a highly concentrated civilian population, military planners decided to orchestrate a series of large-scale outdoor simulations. In September 1950, Camp Detrick scientists launched Operation Sea Spray, a secret biological “vulnerability test” targeted directly at the city of San Francisco, California.
San Francisco was selected as the prime target for this covert maneuver due to its unique geographical and structural layout. The city possessed a prominent coastline, high-density high-rise buildings, and a chronic coastal fog that scientists calculated would easily screen and disguise drifting germ clouds from public view. To execute the operation, the U.S. Navy provided a specialized minesweeper ship equipped with large, high-pressure aerosol hoses. Classified strictly as a confidential military maneuver, the test was executed in absolute secrecy; local municipal authorities and public health officials were never notified. Among the scientists participating in the planning and monitoring of the operation was Frank Olson, a Camp Detrick biochemist who specialized in aerosol delivery systems and the airborne distribution of pathogens.
For six days at the end of September 1950, the Navy minesweeper patrolled the waters just off the California coast, directly spraying massive clouds of a bacterium called Serratia marcescens into the incoming coastal fog. Camp Detrick researchers had specifically selected Serratia marcescens for the experiment because it possessed a distinctive red pigment, which made it exceptionally easy to trace and analyze in samples collected after the release. Furthermore, at the time of the operation, the scientific establishment believed the bacterium was completely benign and incapable of causing any ill health effects in humans.
The results of the dispersion study were immediate and extensive. As the coastal mist rolled inland, it carried the aerosolized bacteria across the entire metropolitan area. According to subsequent air and soil samples gathered by military technicians at forty-three separate monitoring sites, the bacterial cloud successfully exposed all of San Francisco’s 800,000 residents. The path of the biological agent did not stop at the city limits; the traceable red bacteria successfully drifted across the bay, exposing populations in Oakland, Berkeley, Sausalito, and five other adjacent municipal areas.
While the military successfully monitored the physical spread of the pathogen without detection, the test had grave, unintended medical consequences. Within a few weeks of the spraying, eleven patients checked into a local hospital suffering from severe urinary tract infections. Hospital clinicians were deeply alarmed to find that the infected individuals exhibited mysterious red drops in their urine. One of these patients, who was actively recovering from a recent prostate surgery, ultimately succumbed to the infection and died. Local doctors, completely unaware of the Navy’s active military exercise off the coast, were deeply mystified by the sudden outbreak and eventually published a scientific journal article detailing their “curious clinical observation,” for which they could find no biological explanation.
Although the Serratia marcescens release proved to be far more dangerous than the military had originally calculated, the commanders and scientists at Camp Detrick regarded Operation Sea Spray as a resounding tactical success. The military report concluded that the vulnerability test successfully proved that a major biological attack could be launched surreptitiously from the sea and that highly effective, lethal dosages of a pathogen could be distributed over vast, heavily populated urban areas. While the Central Intelligence Agency (CIA) maintained an active interest in the development of biochemical weapons for close-quarters covert actions under programs like MK-ULTRA, the agency played only an observer’s role during Operation Sea Spray, as the execution of large-scale open-air warfare remained the primary domain of the military services.