In 1950 and 1965, vulnerability studies were conducted using two biological warfare scenarios with the use of aerosol. The first scenario was the seaport of San Francisco (open environment) and the second was the subway system of New York City (enclosed environment). In San Francisco, the simulant used was Bacillus globigii(BG). In addition, not only humans were exposed but monkeys and guinea pigs as well. The purpose of the test was to determine if a seaport was vulnerable to a biological warfare attack by line source dissemination (aerosol). It is necessary to understand that line source is very susceptible to meteorological conditions, such as wind. It was learned from this offensive program that liquid cultures were difficult to disseminate into small particles and the disseminating device used required high levels of energy for success. Also, small particles were most effective in causing only respiratory infection. In the scenario involving the New York City subway system, an enclosed environment, meteorological conditions were no longer a factor. The same simulant powder was used as in San Francisco. Lightbulbs were filled with the BG powder and dropped from the back of the trains onto the tracks. Secondary aerosols were created when the trains passed over the powder. The data determined the number of organisms per liter of air and the number of minutes that people were on the train indicating that approximately 80 to 90 percent of the train population would have become infected. In summation, it was determined that domestic terrorists do not have the capability to develop a biological warfare weapon that could result in serious casualties. However, state-supported groups with training and adequate laboratories and funds could develop an agent powder and if used in an enclosed environment could produce thousands of casualties.