It was the ultimate war game for armchair strategists. A dozen experts gathered at Andrews Air Force Base for two days in June for a germ-warfare assault on America's heartland. The exercise was called Dark Winter. The scenario: Oklahoma, Georgia and Pennsylvania have been deliberately targeted with smallpox virus. The mission: to marshal the full resources of the Federal Government and limit the damage. But even though the players included seasoned leaders--former Senator Sam Nunn acting as the President, former presidential adviser David Gergen as National Security Adviser, Oklahoma Governor Frank Keating playing himself--the situation got quickly out of hand. Within two weeks, 16,000 Americans were infected, and 6,000 were dead or dying.
Dismal as that performance was, it all seemed rather theoretical at the time. Not anymore. In the aftermath of the attack two weeks ago, the idea that weapons of mass destruction might be trained on the U.S.--not by such rogue nations as Iraq but by rogues like Osama bin Laden--suddenly seems a lot less unthinkable. Ordinary Americans are waking up in the middle of the night with nightmares about poisoned water supplies and miniature nuclear weapons set off in city streets.
But the chances of such an attack happening anytime soon are remote, most of the terrorism experts consulted by TIME agree. For starters, it takes a lot more money to build, research or steal a weapon of mass destruction than to hijack a plane or unleash a truck bomb. It also takes a lot more brainpower. Says Amy Smithson, a chemical and biological weapons expert at the Henry Stimson Center in Washington: "I can sit here and dream up thousands of nightmare scenarios, but there are a lot of technical and logistical hurdles that stand between us and those scenarios."
The experts also agree, however, that they must rethink their assumptions. The Sept. 11 attacks took patient planning and training; no terrorist group had ever carried out so complex a mission. "I was not at all alarmist about this threat based on the historical record," says Jonathan Tucker of the Monterey Institute of International Studies in Washington, "but given what happened, we need to reassess the threat."
Of the three major types of weapons of mass destruction, biological agents may pose the greatest potential threat, followed by nuclear bombs and chemical weapons. Here's how our experts gauge the relative dangers: