NEW YORK - During a sultry June week in 1966, mysterious men riding the New York subway walked through the train, pausing between cars to drop small objects on the tracks below.
Anybody who got a good look would have recognized the objects as ordinary light bulbs. What other riders couldn't have known is that the bulbs had been pumped full of harmless bacteria meant to simulate anthrax spores.
The scientists of the Special Operations Division, a secret arm of the U.S. biological weapons program at Fort Detrick, Md., wanted to see how easy it would be to expose large numbers of straphangers to a lethal germ.
The answer: pretty easy.
During the 1950s and '60s, Fort Detrick scientists pulled similar stunts all over the United States. They released clouds of bacteria off San Francisco and watched them float over the city. In remote deserts and far at sea, they exposed thousands of guinea pigs and other test animals to anthrax and a half-dozen other scourges. In one experiment, they even pumped bacteria into the Pentagon's ventilation system.
These experiments - described in military documents and a paper by bioweapons pioneer William C. Patrick III - were designed to answer one question: What is the most effective way to deploy biological weapons against the Soviet Union or another Cold War foe?
The U.S. biological weapons program is ancient history, dismantled three decades ago in accordance with the Biological Weapons Convention of 1972. But the things the country's biological warriors learned back then could prove extremely valuable today, as the United States faces its first real bioterrorist threat.
"There was a lot learned," said Leonard Cole, a political science professor at Rutgers University in Newark, N.J., and author of "The Eleventh Plague: The Politics of Biological and Chemical Warfare."
The major problem U.S. weaponeers encountered, and solved, during three decades of research was how to deliver biological weapons on the battlefield.
American scientists would spread a whole menagerie - guinea pigs, monkeys, sheep and other animals - out in the desert or even on floating platforms far at sea. Some experiments used thousands of animals.
Then the researchers would dose the whole lot with a deadly cloud of anthrax or some other pathogen to see how many animals became infected.
"The Army found that it could kill a lot of these animals fairly easily," Cole said.
If they were testing a weapon like Q fever, which was designed to sicken but not kill, the researchers would even include voluntary human subjects. Most were Seventh-day Adventists whose faith did not allow them to serve in combat units.
Those human and animal tests demonstrated that extremely small particles about 1 to 5 microns - 1/25,000th to 1/5,000th of an inch - in diameter are the optimum size for biological warfare.
Particles that small are extremely difficult to produce. To make an aerosol mist so fine requires high-pressure spray equipment with specially designed nozzles. Producing a 1-micron powder requires the ability to freeze-dry and mill anthrax spores into minuscule particles without damaging them. It also requires treating the powder to prevent it from clumping.
Scientists spent years creating the techniques necessary to process and deliver anthrax and other germ weapons dependably. Then they went out and tested them on the American people.
In August 1949, operatives from Fort Detrick slipped themselves and their equipment into the Pentagon by posing as employees of an air quality testing company. Science writer Ed Regis recounts the episode, citing military documents, in his book "The Biology of Doom."
The Pentagon security guards did nothing but help as the infiltrators set up their sprayers, Regis writes. The Army scientists pumped so many harmless bacteria into the building's ventilation system that had the germs really been anthrax spores, a devastating number of America's top military officers would have been dead.
The next year, a series of experiments in San Francisco, explained by germ warrior Patrick, demonstrated that one small slip-up can render a deadly pathogenic cloud perfectly harmless. In the first trial, a ship released a cloud of harmless spores two miles offshore. Gentle winds blew the cloud right through the city. Had the spores been anthrax, the researchers estimated that more than 60 percent of the population would have ended up infected.
But in a second test under different weather conditions, virtually none of the spores reached the city. Yet another experiment also failed, when a cloud of microbes sensitive to ultraviolet light was rendered harmless by the rays of the setting sun.
The 1966 experiment in New York showed that the subway could be an especially lethal place to release anthrax spores or other nasty airborne germs. The rushing trains actually helped the mock attackers by keeping spores aloft and efficiently spreading them through the tunnels.
Concentrations of anthrax spores high enough to endanger anybody in the area could still be measured an hour after the Detrick operatives dropped their bulbs on the tracks, Patrick wrote in his paper published this year by the National Academy of Sciences.
The results of the New York and San Francisco experiments only became public in 1999, when some of the data they produced were declassified by the Defense Department. Even their existence was unknown to the public until the 1970s.
The vast majority of what the biological weapons program learned still remains locked away - in secret libraries at Fort Detrick and in the heads of the few veterans of the program.
"Much of that information is lost," said Scott Layne, a bioterrorism expert at the University of California Los Angeles. "There are few living people remaining who have firsthand knowledge of what is known."
Until recently, it didn't matter much that the offensive biological weapons program was all but forgotten. What did it matter that the United States had forgotten how to deploy weapons it had promised never to use against a country that no longer exists?
Now somebody has mailed high-grade anthrax to the Senate majority leader and an apparently less lethal form of the potentially deadly spores to a number of media outlets. Officials are seriously considering the possibility that the country could be the target of a large-scale biological weapons attack.
According to Layne, it is time to let a few select people into the dusty archives at Fort Detrick. He proposes opening the weapons researchers' inner sanctum to a handful of public health, law enforcement and national security officials.
"There should be maybe five or 10 people around the country who have the relevant need to know who should have access to that information," Layne said. "You have to know what you're dealing with."