Dark Winter's simulated scenario involved an initial localized smallpox attack on Oklahoma City, Oklahoma with additional smallpox attack cases in Georgia and Pennsylvania. The simulation was then designed to spiral out of control. This would create a contingency in which the National Security Council struggles to determine both the origin of the attack as well as deal with containing the spreading virus. By not being able to keep pace with the disease's rate of spread, a new catastrophic contingency emerges in which massive civilian casualties would overwhelm America's emergency response capabilities.

The disastrous contingencies that would result in the massive loss of civilian life were used to exploit the weaknesses of the U.S. health care infrastructure and its inability to handle such a threat. The contingencies were also meant to address the widespread panic that would emerge and which would result in mass social breakdown and mob violence. Exploits would also include the many difficulties that the media would face when providing American citizens with the necessary information regarding safety procedures.

https://en.m.wikipedia.org/wiki/Operation_Dark_Winter