UK announces plans for big Olympic security test

Britain is planning a massive Olympics security exercise around a mock emergency on the London subway system.

The security test announced Monday envisions that an emergency takes place on the busiest days of the 2012 London Olympics, which will run from July 27-Aug.12.

The test Wednesday will involve some 2,500 people. Most of the operation will not be visible to the public, although some people may see a portion of the exercise at a London Tube station. Authorities want to test their communications systems.

Security has long been a key concern at the Olympics. The exercise is also likely to bring up unpleasant memories of the attack on London's transit system on July 7, 2005, which killed 52 commuters.