Operation Dark Winter employed a cast of volunteers... to act out roles following a script in which a terrorist released smallpox in one eastern U.S. city. The result was sobering to an extreme. The public health system virtually collapsed. Hospitals degenerated into chaos. Smallpox spread to twenty-five states and overseas. The national stockpile of vaccines proved to be deeply inadequate. The exercise was called off after four days from the sheer exhaustion of the participants, while the fictional epidemic was still spreading.