Filed at 8:19 p.m. ET

LONDON (AP) -- One July afternoon 40 years ago, unsuspecting commuters on the London Underground were engulfed in clouds of harmless bacteria as part of a secret government germ-warfare test.

If the travelers detected anything in the air, it isn't recorded in the confidential official papers that were released Tuesday by the Public Records Office after the requisite four decades of secrecy.

The papers detail the 1962 trial conducted by government experts to see how far and how fast bacteria would spread through the underground railway system.

A second trial on May 1, 1964, confirmed the 1962 findings that germs could easily travel 10 miles through the underground network of tunnels from a single point of contamination.

Scientists from the Microbiological Research Establishment at Porton Down in southwest England used spores of Bacillus globigii -- described as ``having no undesirable properties'' -- obtained from the U.S. biological weapons research establishment at Fort Detrick, Md.

Thirty grams of the bacteria were put in an ordinary women's face-powder box, ``with some original face powder to provide the correct odor'' and held together with elastic and string.

The scientists selected a stretch of the Northern Line subway south of the River Thames.

On July 26, two pairs of researchers took up their posts at the Tooting Broadway and Colliers Wood station platforms where they were to collect air samples at regular intervals from 1:45 p.m to 4:45 p.m. Their sampling gear was improvised from a pair of footpumps with the valves reversed so that they would suck air in, rather than push it out.

A ``Mr. H.C.P. Havers,'' meanwhile, got into the sixth car of a northbound train at Colliers Wood with his innocent-looking box of germs. And 38 seconds later, as the train reached 31.5 mph, he dropped it out a window.

Swab samples taken in the following days revealed the bacteria had traveled to the Camden Town station -- 10 miles north of the release point, and the farthest point tested.

The heaviest concentration of the spores was found inside rail cars, rather than outside, and the scientists wrote ``it would seem most likely that the spores were carried in the cars.''

A second test was carried out two years later in the same area, but with three sampling stations and 50 percent less of the bacteria.

This time, a battery-operated device worthy of James Bond was employed to test the air inside a northbound train.

``This sampler was silent in operation and readily concealed and operated in a briefcase,'' the report said.

The papers said the spore cloud took less than 10 minutes to arrive at Tooting Broadway'' as opposed to 15 minutes in the first test.

``This simple trial shows that bacterial spores can be carried for several miles in the tube system,'' the files note. ``Trains traveling through such an aerosol became heavily contaminated internally.''

There was no indication of what use would be made of the tests, nor their wider goal.