LONDON — Seconds after two American visitors, Karen Harville and her son, saw a bomb slice off the upper deck of a London bus, they rushed forward to help. But British onlookers grabbed them and pulled them back.
“They were yelling at us: ‘There could be a second blast.’ They were just ordinary people. Not police,” Mrs. Harville said. “It’s my first trip out of the United States, so we had no idea.”
Amid the shouts of horror and scenes of bloodied flesh, the two Americans survived their ordeal with another vivid impression of Britain — one of efficiency and calm in a crisis.
“Everyone was so quick. The police got there and cordoned things off so fast. They made sure that everybody got away. But they didn’t do it in a mean way or a yelling way. Everybody kind of knew what to do.”
As soon as police realized that the city was under attack, they went on emergency alert, shutting down the subway and buses and evacuating passengers.
Authorities requisitioned buses and turned them into ambulances, which carried dozens of casualties to hospital emergency rooms.
The bus explosion — one of four terrorist strikes on London’s public-transport system — took place only yards from the headquarters of the British Medical Association.
Eleven of the country’s most eminent physicians immediately rushed to the scene, said one of them, Dr. Andrew Gerdin.
Dr. Gerdin said two persons died on the sidewalk, despite the best efforts to revive the victims.
In a sad coincidence, the bus was destroyed as it passed Tavistock Square, a monument to peace with a statue of Mahatma Gandhi, a Hiroshima cherry tree and a Holocaust memorial.
In the London Underground, the subway system nicknamed “the tube,” it took a bit longer for teams of rescuers to reach the victims of three explosions.
A carefully orchestrated program called Operation Orange went into force.
All trains, which were carrying an estimated 2 million commuters at the time, pulled in to the nearest station and released everyone.
When the first of the three bombs went off in the Underground, Sally Jones was riding to work in the adjoining tunnel.
The explosion blasted a hole through the wall, and her train shuddered to a halt, the lights went out and she heard screams from the next carriage.
“I thought whatever’s happening to them — probably a fire sweeping through the train — was going to happen to us very soon. People were saying prayers and calling out to God.
“Then, as we just waited there, I thought we were sure to die when the air ran out,” she said.
Rescue workers got there after what she said was a half-hour of hell.
Dozens died in the four attacks, and more than 700 were treated for injuries.
Twenty-one of the dead were trapped on a train close to London’s biggest station, King’s Cross.
“I saw people covered in blood, faces covered with ashes,” said Ronny Browning, 35, as he sipped coffee near the station.
Mr. Browning, who works in a catering business near King’s Cross, had just left the subway platform and was on the escalator when the blast occurred.
“I saw one lady with her whole eye covered in soot, blood and ash. Her face was dripping with blood,” he said.
Only the day before, Mr. Browning had been celebrating in a local bar and in the streets when London was selected to host the 2012 Olympic Games.
“Everything was good. Now I’m thinking: ‘bloody hell.’”