NEVADA TEST SITE, Nev. — Changing realities in a post-Cold War world have caused forced adjustments in America’s nuclear proving ground. In a nine-hour, 250-mile tour of the high-security 1,375-square mile Nevada Test Site — larger than the state of Rhode Island — visitors saw both relics of a bygone era and were briefed on the new defense, environmental and energy programs intended to meet the nation’s needs in the 21st century.

In the opening salvo of the nuclear age, Harry Truman wanted to find a location where through testing and development — the power of the atom could be mastered for scientific and military applications. So the Atomic Energy Commission secretly selected this site, 65 miles northwest of Las Vegas, where 100 atmospheric nuclear tests were conducted in the 12 years after the site opened in 1951.

The site’s methods changed in 1963 when President John Kennedy signed the Limited Test Ban Treaty, literally driving the testing underground. The majority of all nuclear activity in the world, 828 underground tests, was conducted at the site — until 1992, when President George Bush, Sr. placed a moratorium on nuclear testing.

The craters from these years of nuclear blasts speckle the desert floor. While it’s hard to contemplate the damage each bomb could have inflicted if a city had been its target, such was the job of scientists stationed here.

At Frenchman Flat, physicists tested the impact of nuclear blasts on physical structures, constructing and then exploding industrial and residential buildings. Underground garages and shelters were built with different materials to see how much force each could withstand. They also tried to model the effects of blasts on humans, outfitting pigs with miniature military uniforms and locking them in pens to test the effects of the explosions’ intense heat. The pigs were tested, the tour guide said, because their skin is remarkably like that of humans.

The results of these tests are clear to any visitor, with leftover shards of these decimated structures littering the landscape. A railroad bridge was constructed more than a mile away from Ground Zero, the site of detonation. All that is left today are the mangled and partly-melted railroad trestles. Visitors on the tour said these remnants reminded them of the awesome power nuclear weapons bear.

“I’ve seen pictures and read about the destruction of nuclear weapons in books, but actually seeing that railroad trestle made a real impression on me,” said Jim Kirkpatrick, a Wyoming native on a road trip. “Driving around Ground Zero had a unique sense about it.”

Scientists also set off bombs to determine how typical American homes would hold up during a Soviet nuclear attack. Houses built in the Yucca Flat at varying distances from Ground Zero were stocked with all the conveniences of the mid-1950s, and scientists studied each after the blasts. The classic footage of exploding houses comes from this series of tests.

The tour was taken to a house 9,000 feet away from Ground Zero that survived the testing and still stands five decades later.

The site also helped scientists learn more about the limits of nuclear applications. With the power of the atom a mysterious marvel, scientists for a time believed seriously that nuclear weapons could be used as relatively inexpensive tools for peaceful purposes. This notion motivated Dwight Eisenhower to announce his “Atoms for Peace” initiative in 1953. Here, that program met its end.

Named for the biblical parable in which swords are beaten into plowshares, the Plowshare Program explored the possibility of using nuclear blasts to construct dams, dredge canals, clear land for highways and make railroad cuts through mountains. But studies of nuclear excavation — which produced sights like the awe-inspiring Sedan Crater — also created fireball mushroom clouds and deadly levels of radiation, understandably dissuading the use of nuclear warheads to these ends.

New realities at the end of Cold War and the beginning of the War on Terror have shifted research away from such purposes. In 1992, a $44 million underground experiment, co-sponsored by the British, called Project Icecap was four weeks from completion when George Bush Sr. declared a moratorium on testing. The superpowers hoped to study the effects of a nuclear blast on urban high rises. As a result, a several-hundred-foot-tall structure stands alone on the desert floor. Trailers on stilts meant to measure ground movement sits by in case testing is resumed.

And with the war on terror and the recent jump in military spending, use of the site — if not the prospects of renewing Cold War-style testing — is on the rise. A variety of agencies — including the Department of Energy, Department of Homeland Security, Defense Threat Reduction Agency and the national laboratories — have staffs and offices on the site.

In so-called sub-critical tests, scientists have continued to work with different nuclear materials without putting enough together to create a detonation and fallout. The Stockpile Stewardship program allows them to keep the nuclear arsenal modern without testing. A planned 700-ton conventional bomb test set for June was indefinitely postponed by the government last Friday. [See adjacent story]

The Department of Homeland Security has constructed a massive training facility on site to train police, fire and medical first-responders at the federal, state and local levels for various scenarios. These emergency officers come for one-week training courses, which include training on what to do after the release of radiation from a so-called ‘dirty’ bomb.

The federal government picks up the tab for the travel, housing, food and training costs of the law enforcement agencies involved, said John Spahn, a Bechtel contractor and former manger of the HazMat center program at the Nevada Test Site.

At the Incident Experiment Site, the National Center for Combating Terrorism has crashed planes, derailed railroad cars and staged other realistic crisis scenarios. Last week, Las Vegas Fire Department trucks were parked outside one of the mock simulations.

At the HazMat Spill Center that Spahn managed until 2002, first responders can practice cleaning up real chemical spills and containing explosions. More than 10,000 first responders receive specialized training on detecting and responding to weapons of mass destruction.

“You name the three letter agencies,” Spahn said. “They’ve all been out here.”

This helps explain the secrecy still shrouding the site. On the tour, no phones, cameras, recorders or binoculars are allowed. Area 51, the highly-secret government installation, sits on the other side of a ridge at the border of the site. On maps, it is known as Groom Lake. A Predator aircraft — the unmanned aerial drone used extensively in Afghanistan — flew by the tour bus. The planes are operated out of a nearby Air Force base. Humvees with machine gun emplacements rove around the site.

Some tour participants felt the impact of the high level of security.

“I would have liked to have seen more nuts and bolts, but I guess that is off-limits,” said Gary Henderson, a Florida retiree.

Officials said the site is prepared to resume underground nuclear testing in less than two years. The government maintains a staff of 1,200 at the site, a far cry from the once thriving infrastructure that required more than 13,000 supporting a continuous flurry of activity.

While most said they enjoyed the tour and were proud of the work the government has done here, one participant worried that the tours don’t tell the whole story.

“It’s good for people to come get educated, but you have to be careful about how much information you take from here,” said Michele Mason, a postdoctoral fellow at Stanford’s Freeman Spogli Institute for International Studies. “There’s a lot of information that is being left out.”