Memories of 50 years at Ground Zero

At exactly 5:29:45 Mountain War Time on Monday 16 July 1945, a blinding 19-kiloton explosion occurred in the high desert north of Almagordo, New Mexico. It would lead to a quick end to the war in the Pacific - and usher in the atomic age.

An estimated 3,000 people yesterday marked the 50th anniversary of the first atomic bomb's detonation at Ground Zero, the Trinity Site on the White Sands Missile Range.

There were no ceremonies or speeches at the 15ft blackened obelisk that marks where the 100ft tower from which the bomb was dropped once stood. A protester who said he was from near Three Mile Island in Pennsylvania, the scene of a 1979 nuclear accident, was arrested after he threw a liquid he called "symbolic blood" at the obelisk. The tower itself was vapourised in the atomic blast.

The plutonium fission bomb - known as the "gadget" to the Manhattan Project physicists led by J Robert Oppenheimer, who developed it 200 miles away at Los Alamos - has left few traces. A 1,200ft crater has long been filled in and radioactive fallout removed by the Atomic Energy Commission.

The 51,500-acre area, designated a national historic landmark in 1975, is open to the public twice a year. Visitors yesterday were able to root though the scrub land for bits of tritinite, a glassy green material formed by the fusion of sand at the high temperatures of the blast.

The characteristic multicoloured column and subsequent mushroom-shaped cloud rose 40,000ft into the early morning skies.

At the nearby McDonald ranch house, where the bomb had been assembled, and from instrumentation bunkers 10,000 yards from Ground Zero, physicists and invited observers watched the blast. "It looked like a giant magnesium flare which kept on for what seemed like a whole minute, but was actually one or two seconds," recalled Hans Bethe, a scientist on the project. "The white ball grew and, after a few seconds, became clouded with dust."

Others were impressed by the heat. "Suddenly, not only was there a bright light but, where we were, 10 miles away, there was the heat on our faces," said Dr Philip Morrison. "Only minutes later, the sun rose and again you felt the same heat."

Although no information was released until after the bombing of Hiroshima on 6 August, people in New Mexico knew something had happened.The shock broke windows 120 miles away and could be felt as far away as 160 miles. At the time, army officials simply stated that a munitions dump had blown up.

Many visiting the McDonald house remember the bomb's construction. Brigadier- General Thomas Farrell recalled taking the delivery of two spheres of plutonium at the ranch house.

"I took this heavy ball in my hand and felt it growing warm,'' he said. "For the first time I began to believe some of the fantastic tales the scientists had told me about this nuclear power."

Immediately after the test, parts for the bombs that would be dropped three weeks later on Hiroshima and Nagasaki were shipped to the Pacific island of Tinian for assembly.

Two scientists who worked on the project said they had no regrets about their involvement. "It did, you know, stop the war. We felt we were doing a good thing," said Berlyn Brixer, 84, who photographed the event.

Curiosity drew many of the visitors to the site yesterday. Cheryl Swannack, a self-described "peacenik", had driven from nearby Las Cruces to see it. "I'm almost 50 years old," she said, "and ever since I have been alive there's been a bomb."