LONDON — Four men were each given life sentences for taking part in a botched suicide attack on London’s public transport system on July 21, 2005, two weeks after bombers murdered 52 commuters.

Muktar Said Ibrahim, Yassin Hassin Omar, Hussein Osman, and Ramzi Mohammed were convicted by a jury in London on July 9 of conspiracy to murder. The Muslim men were charged with attacks on three trains and a bus. No one was hurt when the explosives failed to detonate completely.

“This was a viable, nearly successful attempt at mass murder,” Justice Adrian Fulford said as he sentenced each man to spend at least 40 years in jail. “It was long in the planning and coming soon after” July, “designed for maximum impact.”

The July 21 attack came as Londoners were recovering from the deadliest attacks on the city since World War II and the first suicide bombings in Western Europe. On July 7, 2005, four other Muslims had blown themselves up, killing commuters in attacks also aimed at three trains and a bus.

Throughout the case, the men claimed it was a hoax designed as a protest against the war in Iraq. The prosecution said the men had incompetently mixed the chemicals used in their bombs and had planned to kill hundreds of people.

Justice Fulford said he had “no doubt” the men were “acting under the overall control of Al Qaeda” and were part of a “parallel but separate” cell as the July 7 bombers. He said the bombs had been designed to explode.

“Had they succeeded at least 50 people would have been killed, hundreds would have been injured and thousands would have had their lives damaged,” he said.

With a minimum term of 40 years, the men may never be released from jail, the judge said. Arthur Burton-Garbett, a 72-year-old antique bookseller who was on the train that Mohammed had attempted to blow up near the Oval underground station, said the judge’s remarks were “chillingly accurate.”

“If I could have given them execution, I would have,” he said after the hearing.

The four men went on the run following the attacks, which were also attempted on a bus in Hackney and on trains near Warren Street and Shepherd’s Bush stations. Mr. Omar, who escaped by bus dressed in a full-body dress called a burka, was arrested in Birmingham six days later. Mr. Osman traveled to Paris by train and on to Italy, where he was detained and extradited. Meassrs. Mohammed and Ibrahim were arrested in London on July 29.

Justice Fulford said prosecutors would retry two other men in the case, Manfo Kwako Asiedu and Adel Yahya, after jurors failed to reach a verdict on the charges against them.