For a period of 20 years between 1949 and 1969, the U.S. army had conducted more than 200 secret biological warfare tests over populated areas, and among the first was in the 1950s off the coast of San Francisco Bay.

A boat went back and forth for a couple of days in September spraying a bacteria called Serratia marcescens.

In his book, “Clouds of Secrecy,” Cole said it was touted as harmless bacteria, but that wasn’t the case.

Nearly all of San Francisco received 500 particle minutes per liter. In other words, nearly every one of the 800,000 people in San Francisco exposed to the cloud at normal breathing rate (10 liters per minute) inhaled 5,000 or more particles per minute during the several hours that they remained airborne.

Cole said a careful inspection of the medical literature would have shown that bacteria was responsible for not only making some people ill over the course of 50 years, but also in a few instances caused their death.

“Here’s an experiment involving human subjects, but the purpose of the experiment was not to see anything about the survival of the individuals,” Cole said.