On the morning of July 7, 2005, bombs are detonated in three crowded London subways and one bus during the peak of the city’s rush hour. The synchronized suicide bombings, which were thought to be the work of al-Qaida, killed 56 people including the bombers and injured another 700. It was the largest attack on Great Britain since World War II. No warning was given.

The train bombings targeted the London Underground, the city’s subway system. Nearly simultaneous explosions, at about 8:50 a.m., occurred on trains in three locations: between the Aldgate and Liverpool Street stations on the Circle Line; between the Russell Square and King’s Cross stations on the Piccadilly Line; and at the Edgware Road station, also on the Circle Line. Almost an hour later, a double-decker bus on Upper Woburn Place near Tavistock Square was also hit; the bus’s roof was ripped off by the blast.

The attacks took place as world leaders, including British Prime Minister Tony Blair, were meeting at the G8 summit in nearby Scotland. In his remarks after learning of the blasts, Blair called the attacks barbaric and pointed out that their taking place at the same time as the G8 summit was most likely purposeful. Later, he vowed to see those responsible brought to justice and that Great Britain, a major partner with the U.S. in the war in Iraq, would not be intimidated by terrorists.

Of the four suicide bombers, three were born in Great Britain and one in Jamaica. Three lived in or near Leeds in West Yorkshire; one resided in Aylesbury in Buckinghamshire. Al-Qaida officially claimed responsibility for the attacks on September 1, 2005, in a videotape released to the al-Jazeera television network.

Two weeks later, on July 21, 2005, a second set of four bombings was attempted, also targeting the city’s transit system, but failed when the explosives only partially detonated. The four men alleged to be responsible for the failed attacks were arrested in late July.

An estimated 3 million people ride the London Underground every day, with another 6.5 million using the city’s bus system.