The cold, dry wind blasting from the Arctic was perfect. A secret Army experiment had waited weeks in 1957 for just such gusts to spread a new type of cloud - a toxic one.

Germ warfare researchers at Utah's Dugway Proving Ground planned to drop easy-to-trace particles of cadmium sulfide in that wind and - with a little luck - watch them scatter throughout the Midwest from Canada to the Gulf of Mexico.That would prove they could do the same with germ weapons that could be used, for example, to destroy an enemy's wheat crop by dropping disease spores from airplanes flying far away in the Arctic.

While the wind was perfect that November 1957, just about everything else was not. Airplanes broke down. Delays came. And when chemicals were finally dropped, the wind changed. Instead of spreading particles from Canada to the Gulf of Mexico as planned, they spread from South Dakota east to the Atlantic.

Still, the test was dubbed "a partial success."

So began Operation LAC, short for Large Area Coverage. It eventually would send huge, potentially toxic clouds over most states east of the Rockies, large chunks of Canada and maybe even the Caribbean.

Newly released documents show that four tests were designed "over a test site comprising roughly that region of the continental United States lying east of the Rocky Mountains. Sampling stations were established in an area of approximately 1.9 million square miles."

Monitoring stations in 40 states

To be exact, 175 monitoring stations were set up in 40 states to capture and count particles of cadmium sulfide and zinc sulfide that would be dropped from airplanes.

Most were next to regular airport weather stations then operated by the old U.S. Weather Bureau or the Civil Aeronautics Administration. Several more were set up at fire stations in some larger cities to see how particle movement within a city may vary. Some L-23 airplanes were equipped to monitor particle travel in flight.

The Army obtained letters from the chiefs of the weather bureau and the CAA ordering cooperation among employees. Dugway researchers then visited each site to set up the stations and train employees.

At each station, a device would pull 12.5 liters of air a minute through a black crepe paper filter about 3 inches in diameter. The filter would be changed every four hours during the experiment and sent to Dugway for examination.

Test results studied at Dugway

At Dugway, filters would be placed under a microscope with ultraviolet light. The cadmium sulfide particles would fluoresce and then easily be counted. Information would allow researchers to determine how far the chemical clouds traveled and in what concentrations.

Other parts of sometimes meticulous planning for Operation LAC included having the U.S. Army Biological Warfare Laboratories at Fort Detrick, Md., design a machine that would fit into the paratrooper floor door of a C-119 aircraft and evenly suck up and distribute chemicals into the plane's slipstream at a top rate of 37.5 pounds per minute.

Next, researchers figured what kind of weather would most likely spread such particles the farthest.

They settled on a dry, cold Arctic blast of wind with an "inversion cap" to keep particles from moving into high altitudes - forcing them to mix thoroughly with lower air. They didn't want rain or snow, because they tend to break up chemical clouds. And they needed a strong wind to move their cloud a great distance.

While documents don't say how high planes would fly, it hints that drops may have come from relatively low altitudes because some "dog leg" paths for airplanes had to be drawn to avoid mountains and ensure dropping from uniform height. Also particles were dropped under "thermal caps" described to be sometimes as low as 2,000 feet above the terrain.

Dugway spokesman Dick Whitaker, however, said drops were made from "high altitude."

When time for the tests arrived, Dugway officials set up Operation LAC headquarters at the U.S. Weather Bureau in Kansas City, where all the necessary weather information was instantly available.

Test 1

In late November 1957, the type of weather sought was developing. On Nov. 26, the weather bureau predicted winds that expected to "extend from the Canadian border to the Gulf of Mexico" would be their strongest on Nov. 29 - so the first test was scheduled for the evening of that day.

But one of three planes that was to perform in-the-air monitoring broke down and could not reach the rendezvous point in Minneapolis until Nov. 30. Army documents said delays waiting for it caused the experiment to miss the best weather possible. The wind was shifting as the drop was finally begun, and delays in weather maps then did not allow officials to catch it in time.

A propeller-driven C-119 "flying boxcar" on loan from the Air Force finally took off with a cargo hold full of cadmium sulfide on a route between International Falls in northern Minnesota and western South Dakota.

Inside were stacks of 50-pound cartons filled with powdery tracer chemicals. The Army refused to release information about the exact formula of those chemicals, but scientific literature said the Army typically used a mixture that was 80 percent zinc sulfide and 20 percent cadmium sulfide.

Photos show five men walking among those stacks of dusty chemicals. They're wearing parachutes but no respirators or gloves.

While they hoped particles would travel south to the Gulf of Mexico, they went east to the Atlantic. The "thermal cap" also disappeared a day later and "allowed an unlimited upward diffusion in the later stages of the cloud travel."

Still, an Army historian later wrote, "It was partially successful since some stations 1,200 miles away in New York state detected the particles." Army maps show the cloud also likely covered parts of North and South Dakota, Minnesota, Iowa, Wisconsin, Michigan, Ontario, Quebec, New Hampshire, Vermont, Maine and out to the Pacific.

Test 2

The second test came a little over two months later on Feb. 9, 1958 - after starting and stopping twice because of shifting weather. An airplane again broke down, but this time researchers did not wait for it to be repaired and again risk a wind change.

This time the C-119 flew 200 miles between Minneapolis and eastern South Dakota. This time, researchers had good luck with the winds.

In two days, particles spread from Minnesota to the Gulf of Mexico. Also, "As the air mass moved south, the front broadened so that the line of particles 200 miles long at the aircraft's path had spread out to 600 miles at the gulf," historians wrote.

Documents also said researchers were pleased that "a well-defined thermal cap (developed, which) averaged about 2,200 feet above terrain. . . . The cold air beneath the thermal cap was either conditionally unstable or, at times, completely unstable, and these features usually indicate a thorough mixing of the air beneath the inversion cap.

"This polar outbreak developed into a strong persistent system, and the movement of the air mass carried the aerosol cloud south out over the Gulf of Mexico."

Maps show that cloud ended up covering parts of Minnesota, South Dakota, Nebraska, Iowa, Missouri, Illinois, Kansas, Oklahoma, Kentucky, Tennessee, Mississippi, Alabama, Louisiana and Texas.

Test 3

The next test took place on March 21, 1958, with a long flight dropping particles between Abilene, Texas, and Toledo, Ohio. Army maps show particles spread across the entire southeastern states to the Atlantic and Gulf of Mexico toward the Caribbean.

Documents said a random weather pattern was selected for this test, with wind patterns that appeared much like the other tests but without a "thermal cap."

Documents added, "The wind field for this trial was stronger and more persistent than would normally occur in most random situations, and it carried the aerosol cloud out into the Atlantic Ocean and Gulf of Mexico."

Maps showed it likely covered parts of Ohio, West Virginia, Virginia, Kentucky, North and South Carolina, Tennessee, Georgia, Florida, Alabama, Mississippi, Arkansas, Louisiana, Texas and Oklahoma.

Test 4

The final test of Operation LAC occurred on April 26, 1958, with a dog-leg-shaped flight from Detroit to Springfield, Ill., and Goodland, Kan.

Documents said researchers were now not too picky about waiting for perfect winds from the Arctic this time. "The season of strong polar outbreaks was past and the first one to appear was chosen." Weather included some thunderstorm activity that caused locally strong gusty winds, showers and hail.

Maps suggest the particle cloud covered parts of Maryland, Pennsylvania, West Virginia, Virginia, North and South Carolina, Alabama, Tennessee, Kentucky, Ohio, Indiana, Illinois, Missouri, Arkansas, Oklahoma, Kansas, Colorado, Nebraska and Wyoming.

Army says `success'

After spreading particles so far in its four tests, the Army deemed Operation LAC a success.

Besides the three until-now-secret volumes that Dugway researchers wrote about the tests, Stanford University researchers used data from it to write a paper titled, "An Analysis of Continental Scale Aerosol Cloud Travel," which was classified as secret. Biological Warfare Laboratories researchers wrote a paper about the performance of their disseminating machine.

And an Army historian wrote in 1959, "These tests proved the feasibility of covering large areas of a country with BW (biological warfare) agents. . . . While the tests were a great step forward, they did not provide the corps with nearly as much data as the corps would like. . . . The corps planned further tests."