Police escorted bloodied passengers up to ambulances, cordoned off the street near a stricken London subway station and rushed off to find an half-exploded knapsack.

But it was all just an Olympic security drill.

Britain's police, fire and ambulance services tested their ability Wednesday to deal with a terrorist attack during the London Olympics, swooping on a disused subway station for a drill that revived painful memories of the 2005 bomb attacks on London's transit system.

The two-day test — called "Forward Defensive" — started at the Aldwych subway station, which has been closed to commuters since 1994. The London Underground maintains the station so it can be used in movies and rented for parties. Its narrow staircases, looping track, tunnel and platform make it the perfect location to simulate dealing with an emergency in close quarters.

"If there are mistakes, this is the time to make them, not when there's a real incident," said British Transport Police spokesman Simon Lubin.

For participants, the test evoked memories of the July 7, 2005, London transit attacks, when four suicide bombers killed 52 commuters on three subway trains and a bus. That attack came a day after London was awarded the 2012 Olympics.

One of the primary areas under review was the communications ability of emergency workers, different police services, government ministers and transport officials. Official reports and an inquest had criticized the emergency services' response to the 2005 bombings.

"I think we have obviously since that event (the 2005 attack) learned a number of lessons," said Howard Collins, chief operating officer of London Underground. "A lot of investment has happened, not only in the Tube but also in those emergency services, new radio systems, new equipment. So we are going to see all those new things tested."

The security exercise involving 2,500 people simulated an attack on one of the busiest days during the 2012 London Olympics. Authorities said the scenario involved a partially exploded knapsack on the Underground.

Among those watching the drill was office worker Michelle Bailey, 31.

"It brought it back to me, what happened in 2005," she said. "At least they're prepared, this time."

The Olympics present a massive security concern. Ever since 11 Israeli athletes and coaches died in an attack at the 1972 Munich Games, the event has been seen as a magnet for groups anxious to publicize their cause.

British authorities have planned for a threat level for the London games of "severe," meaning an attack is "highly likely."

British authorities have refused to discuss whether there has been any particular threat to the London Olympics, which open July 27 and end Aug. 12.