They rallied Saturday at the birthplace of the atomic bomb, outside the national labs that feed today's nuclear arsenal, on the tiny island where the Enola Gay (search) took off for Hiroshima with its deadly payload, and in the nation's capital.
Bombing survivor Koji Ueda attended a rally in the Los Alamos (search) park where there were research laboratories when the Manhattan Project developed the world's first atomic bomb.
"No more Hiroshimas. No more Nagasakis," Ueda said. "We send this message to our friends all over the world, along with a fresh determination of the 'hibakusha' (atomic bomb survivors) to continue to tell about Hiroshima and Nagasaki, aiming at a planet set free of wars of nuclear weapons."
In Oak Ridge, Tenn., 15 protesters from a group of more than 1,000 were arrested for blocking a road outside the heavily guarded weapons factory that helped fuel the bomb during World War II.
At the Nevada Test Site, about 200 peace activists, including actor Martin Sheen, gathered for a nonviolent demonstration outside the gates. Dozens were given citations and released after crossing police lines. There was no immediate count of exactly how many were detained.
In California, hundreds of activists marched to the gates of Lawrence Livermore National Laboratory (search), some holding sunflowers and others hoisting a 40-foot inflatable "missile."
The city of Hiroshima, meanwhile, marked the anniversary with prayers and water for the dead.
At 8:15 a.m., the instant of the blast, Hiroshima's trolleys stopped and more than 55,000 people at Peace Memorial Park (search) observed a moment of silence that was broken only by the ringing of a bronze bell.
Ueda, who was 3 when the bomb was dropped on Hiroshima, was joined at Los Alamos by Masako Hashida, who was 15 and working in a factory a mile from where the second bomb fell three days later on Nagasaki.
In an interview with The Associated Press, Hashida recalled hearing a loud metallic noise and then seeing waves of red, blue, purple and yellow light. She said she lost consciousness and awoke outside the twisted metal ruins of the factory, which had made torpedoes used in the attack on Pearl Harbor.
She saw a person trying to stand, with burns and swelling so severe it was impossible to tell if it was a man or a woman.
In the Los Alamos park where research laboratories stood during the Manhattan Project (search), placards carried anti-war slogans including "No More War for Oil and Empire."
A group of veterans offered an opposing message across the park from the more than 500 activists. One sign read: "If there hadn't been a Pearl Harbor, there wouldn't have been a Hiroshima."
In Washington, G.R. Quinn, 54, of Bethesda, Md., held a sign across from the White House reading: "God Bless the Enola Gay," referring to the B-29 that dropped the first bomb. Nearby, about three dozen peace activists declared President Bush was not doing enough for nuclear disarmament.
More than 300 activists marched to the gates of Lawrence Livermore National Laboratory, about 50 miles east of San Francisco, some planning to plant the sunflowers they outside its fence.
The facility was created years after the bombs were dropped, but it has helped develop nuclear weapons in the nation's current arsenal.
A group of U.S. veterans met with atomic bomb survivors on the tiny island of Tinian in the Northern Mariana Islands (search) to commemorate the anniversary. The island was the launching off point for the plane Enola Gay, which dropped its deadly payload over Hiroshima in 1945.
About 70 veterans and several survivors agreed to use their final years to advocate world peace and call for an end to nuclear proliferation.
The uranium for the bomb dropped on Hiroshima was supplied by the Y-12 nuclear weapons plant in Oak Ridge, which continues to make parts for every warhead in the country's nuclear arsenal.
More than 1,000 demonstrators carrying signs and beating drums marched outside the Y-12 gates in the largest peace protest ever in the city, which was built in secrecy during World War II. Fifteen protesters were arrested for blocking the road about 100 yards from the entrance, a misdemeanor.
"Those of us who live here have a special, maybe accidental, responsibility to think about the hard sides of these questions," said Fran Ansley, a University of Tennessee law professor.