Are New York subway riders vulnerable to an attack with sarin, the nerve gas that killed 10 and injured more than 5,000 in Tokyo?
Yes, of course.
In fact, back in 1966 the U.S. Army showed conclusively that the subway system was vulnerable to attacks with chemical and biological agents.
In the 1950s and 1960s, the Army conducted hundreds of tests in New York and other populated areas.
Bacteria and chemical particles were sprayed from a boat off San Francisco, from trucks driving through Minneapolis, from slow-flying airplanes above the Midwestern states. The object was to see how the particles spread.
For five days, the Army conducted a bizarre test in New York's subway system. It released relatively harmless bacteria called Bacillus subtilis, which were mixed with charcoal particles, a simulated chemical agent.
The testers filled light bulbs with bacteria and charcoal, then shattered the bulbs on ventilating grills at sidewalk level and tossed them on the tracks as trains entered the station.
Confirming what should have been obvious without testing, the bacteria and charcoal spread as trains whooshed in and out. More than one million commuters were exposed to them. The test was deemed successful.
According to the Army's report, "A large portion of the working population in downtown New York City would be exposed to disease if one or more pathogenic agents were disseminated covertly in several subway lines at a period of peak traffic."
The test agents were far less harmful than those that would be used in war, but still posed health risks.
When the public learned about them from news reports and Senate hearings in the 1970s, the tests were condemned. The Army said no one was made ill, but conceded that it did not monitor anyone exposed.
After World War I, chemical and biological weapons were deemed pariahs. For most of the period, international treaties reinforced the sense of repugnance that had almost wholly forestalled their use.
Not until the mid-1980s, when Iraq turned chemical weapons against Iran, had any nation used such arms so extensively and for long periods. Content to see them battle each other, the world largely remained silent about Iraq's chemical transgressions.
Deferring to the Arab states, U.N. Security Council resolutions that called for an end to hostilities avoided condemning Iraq for using chemical weapons.
By the time Iran capitulated, in 1988, the lid of moral restraint had been lifted. More than 20 countries now had chemical weapons programs.
One result was that U.S. and allied forces in the Persian Gulf war anticipated chemical and biological attacks. The Army says none occurred, but some members of Congress are skeptical.
True, concern about these weapons has belatedly increased efforts to ban them, notably with the new Chemical Weapons Convention, which the United States has yet to ratify. But ratification is only one step.
Condemnation and punishment of any nation that harbors chemical or biological weapons must be swift and sure. Iraq's use of chemical arms, and now the expanding list of countries with chemical weapons programs, has created psychological as well as physical danger.
The more nations that acquire these unconventional weapons, the more they may be considered conventional.
The best way to minimize the likelihood of their use is to foster the ethos that largely prevented their use for 70 years.
An invigorated international effort to ban chemical and biological weapons is the surest lesson the past can teach.