The Next Threat?

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.

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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:

Chemical Weapons
Ranging in sophistication from rat poison to powerful nerve toxins, chemical weapons are by far the most popular among terrorists. That's because the raw materials are relatively easy to get, and the finished products don't have to be kept alive. But chemical weapons aren't well suited for inflicting widespread damage. Unlike germs, chemical agents can't reproduce, observes Tucker. "You have to generate a lethal concentration in the air, which means you need very large quantities." To kill a sizable number of people with sarin, for example, which can be absorbed through the skin as a liquid or inhaled as a vapor, you would need something like a crop-dusting plane--which is why investigators last week were so alarmed to find a manual for operating crop-dusting equipment while searching suspected terrorist hideouts. Still, to attack a city with sarin, you would probably have to fly thousands of pounds back and forth over heavily populated areas--not something easily done, especially now.

Indeed, the most devastating nonmilitary chemical attack ever, by the Aum Shinrikyo cult in Tokyo in 1995, killed only a dozen people. One reason is that the delivery method was crude: cultists dropped plastic bags of sarin (smuggled in lunch boxes and soft-drink containers) on a subway platform and pierced them with umbrella tips. Also the amounts were relatively small. Says Smithson: "Any bozo can make a chemical agent in a beaker, but producing tons and tons is difficult." Aum Shinrikyo tried to make the stuff in bulk, recruiting scientists and spending at least $10 million, but it failed.

Terrorists could try to tap into the more ample supplies of chemical arms believed to be stockpiled by Iraq and other outlaw states. But Tucker points out that the leaders of such countries would probably be reluctant to let weapons banned by international treaty out of their direct control; if they were traced back it could lead to swift retaliation. "We know Saddam Hussein is ruthless," he says, "but generally he is not reckless."

Nuclear Weapons
More than 25 years ago, in an eerie foreshadowing of the World Trade Center attack, the writer John McPhee explored with nuclear physicist Ted Taylor the question of how you could topple the Twin Towers with a small atomic bomb. Positioned correctly, McPhee reported, a nuke a tenth as powerful as Hiroshima's could knock a tower into the Hudson River.

But that assumes you could manufacture the bomb and put it into position. A terrorist would first have to get hold of some sort of fissionable material--ideally, says Princeton University nuclear proliferation expert Frank von Hippel, enriched uranium. North Korea, Iraq and Libya are believed to have uranium stockpiles but would probably be loath to let them go. A more likely source is the former Soviet Union, where bombmaking supplies are plentiful, the economy is in upheaval, and security has collapsed.