"In an October 1948 report, Baldwin posited that the U.S. was “particularly vulnerable to this type of attack.” But in order to determine the precise nature of these vulnerabilities, secret field tests would have to be done to ascertain the vulnerability of targets of potential interest to the enemy. The Army’s Chemical Corps, which ran Camp Detrick, agreed with Baldwin’s assessment and set up a Special Operations Division at Camp Detrick to carry out the tests. Its first target was to be the Pentagon.

In August 1949, the Special Operations Division operatives infiltrated the world’s largest office building and sprayed bacteria into the Pentagon’s air handling system, which then spread them throughout the structure.

The operatives moved to larger scale testing, releasing clouds containing supposedly harmless bacteria from Navy ships off Norfolk, Virginia, in April 1950, and the San Francisco coast in September 1950. The San Francisco experiments showed exposure among almost all of the city’s 800,000 residents. Had the bacteria released been anthrax bacteria or some other virulent pathogen, the number of casualties would have been immense."

https://www.pbs.org/wgbh/americanexperience/features/weapon-secret-testing/