No civilians were believed to have been exposed to live chemical or biological agents during the tests, which were conducted between 1962 and 1973 in the United States, Canada and Britain, said William Winkenwerder, assistant secretary of defense for health affairs.

But he said real organism were used in tests to simulate biological agents such as anthrax, and large numbers of civilians may have been exposed to them.

"The place with the likely largest exposure might have occurred would have been in Hawaii," Winkenwerder said. "We don't know the numbers there but it could have been into the thousands of people that might have been exposed."

One test involved spraying an anthrax-like organism, Baccillus globigii or BG, from fighter jets off Oahu.

BG was regarded as unlikely to cause disease in healthy humans but has been associated with acute infections of the ear, brain lining, urinary tract, lung, heart valve and bloodstream in people with compromised immune systems.

Other simulants used in tests that were considered benign included such organisms as e-coli bacteria and serriatia marcescens that are now recognized as harmful.

"We clearly don't have any evidence that anyone died as a result of these operational tests," Winkenwerder said.

Besides Hawaii, Winkenwerder also said there may have been civilian exposure to simulants used in tests near Fort Greely, Alaska; Yeehaw Junction, Florida; and the island of Vieques in Puerto Rico.

It was unclear which simulants civilians may have been exposed to or which tests may have resulted in exposures.

The Pentagon released declassified fact sheets on 27 tests that were conducted during the 1962-1973, disclosing for the first time tests that were conducted on land as well as at sea.

The release follows disclosure over the past year of other Cold War-era tests in which manned US ships were sprayed with chemical and biological agents.

The newly disclosed series include tests in which lethal VX and Sarin nerve gas were sprayed or dispersed in bombs in snow-covered Alaskan woodlands and Hawaiian rainforests.

One 1965 test called Magic Sword involved releasing uninfected mosquitoes from a ship off the coast of Baker Island in the Pacific.

The goal was "to obtain information on mosquito biting habits, mosquito trap technology, and operational and logistical problems associated with the delivery of mosquitoes to remote sites," the Pentagon said.

The tests had names like Big Tom, Sun Down, Fast Tan, Devil Hole and Green Mist.

In Elk Hunt, a 1964 test conducted near Fort Greely, mines filled with VX nerve gas were detonated under ground and underwater.

Troops in impermeable rubber outfits and masks then traversed the area to see how much VX would stick to their clothing.

In a second phase of the testing, troops crossed contaminated terrain in vehicles to determine how they would be affected.

"The reasoning behind all of these (tests) is not altogether clear from the records that we have, but certainly it was to evaluate our own protective capabilities, and procedures and tactics as well as how an offensive use of that agent might affect," Winkenwerder said.

About 500 US troops were involved in the land-based testing, only a fraction of the 5,000 military personnel who were involved in the sea-based testing, many of them on warships that were doused with agents or simulants.

The Veterans Administration has sent letters to more than 1,300 veterans involved in the sea-based testing.

So far 55 have come forward to file claims for benefits but their ailments are typical for people their age, the officials said.

SPACE.WIRE