Military test security in UK ahead of Olympics
A big security exercise is underway to check military plans to protect the millions of people coming to see the Olympics.
Royal Air Force fighter jets and helicopters are practising flying over London this week to make sure they're ready to respond to any security threat during London 2012.
The Typhoon jets can fly at almost twice the speed of sound, meaning they can get quickly to a plane if it's hijacked.
Defence Secretary Phillip Hammond reckons people shouldn't worry though, saying: "There is no specific threat to the Games but we have to be ready to assist in delivering a safe and secure Olympics for all to enjoy."