The Pentagon has acknowledged for the first time that it conducted secret Cold War testing with chemical and biological agents on American soil.

Defense officials estimate only some 500 U.S. military personnel participated in the land-based tests of the lethal substances, most conducted in remote areas like Alaska.

But they also acknowledge an undetermined number of civilians may have been exposed to other tests in the United States involving harmless, simulated chemical and biological materials.

Still, the officials stress the testing carried out in the 1960s and early 1970s was not intended to evaluate the effects of dangerous agents on humans and they say no one died as a result of their participation.

Instead they say the testing was designed to evaluate protective equipment along with military tactics and procedures. They also say authorities at the time hoped to learn more about the behavior of agents ranging from Sarin and VX gas to various germ warfare agents under different climatic and environmental conditions.

The details are revealed in newly-released, declassified documents involving 27 Cold War era tests carried out under the auspices of a program known as Project 112. The release of the information is in response to the concerns of some U.S. veterans that they might have suffered adverse health consequences from their participation in the testing program.

Defense officials say that despite complaints from some 50 veterans, no conclusive links have been established between participation in the tests and any specific ailments.

The tests were carried out in Alaska, California, Florida, Hawaii, Maryland and Utah along with Puerto Rico, Canada and Britain. The tests carried such exotic names as "Tall Timber," "Green Mist," and "Rapid Tan."

Additional testing involving larger numbers of military personnel was carried out at sea. The Pentagon disclosed earlier this year some 5,000 sailors on U.S. warships were exposed to deadly agents to determine the vessels' potential vulnerability to chemical or biological attack.

The U.S. Department of Veterans Affairs is working to contact all veterans involved in the testing to advise them of medical care and benefits they might be entitled to.