Operation Sea-Spray: When the U.S. Military Sprayed a City with Bacteria

In 1950, the U.S. Navy conducted a secret biological warfare experiment called Operation Sea-Spray—and the test subject was none other than San Francisco.

Over several days, military ships off the coast released clouds of Serratia marcescens, a bacteria believed to be harmless, to test how a biological agent might spread in a real urban environment. The bacteria blanketed the city, infiltrating homes, businesses, and hospitals—without the public’s knowledge or consent.

Shortly afterward, a spike in rare infections occurred at a local hospital, and one man died. Though the military denied a connection, the incident raised serious ethical and legal questions.

It wasn't until decades later that the test was revealed, sparking outrage and reinforcing fears about secret government experiments on civilians during the Cold War.

Operation Sea-Spray is a chilling reminder: sometimes the test subject is you—and you don't even know it.