London launched a major military exercise Wednesday to check security responses for the 2012 Olympics, as the final wave of test sports events got under way.
Royal Air Force (RAF) Typhoon fighter jets flew into the capital to herald the start of Exercise Olympic Guardian, a nine-day training operation to test the response to a possible attack from the air during the Games.
Military helicopters were to be stationed around the capital, including some on the amphibious assault ship HMS Ocean in the River Thames, and others carrying sniper teams.
The Typhoons will be operating at RAF Northolt in west London -- the first time fighter aircraft have been stationed at the military airbase since World War II.
AWACS surveillance planes and air-to-air refuelling aircraft will also be airborne.
"Whilst there is no specific threat to the Games, we have to be ready to assist in delivering a safe and secure Olympics for all to enjoy," said Defence Secretary Philip Hammond.
"The fact that our state-of-the-art Typhoons will be stationed at RAF Northolt underlines the commitment of the Ministry of Defence and our armed forces to keeping the public safe at a time when the world will be watching us."
Britain's regular air defence includes round-the-clock radar with Typhoons on high alert.
Meanwhile, the Olympic Park in Stratford, east London, was getting its biggest test of readiness for the Games as the final wave of test events got under way.
From Wednesday until Tuesday, five venues will stage events in three Olympic and three Paralympic sports.
Assisted by 11,000 staff, more than 140,000 spectators will watch 3,000 athletes take part in hockey, wheelchair tennis, water polo, athletics, boccia and Paralympic athletics.
The international invitational hockey tournament leads the way, starting Wednesday.
World number one Australia, Olympic champions Germany, Britain and India are competing in the men's event, while World Cup holders Argentina, China, Britain and South Korea are playing in the women's tournament.
The British university athletics championships will take place in the main Olympic Stadium from Friday to Monday, and on Saturday the sport will be mixed with a concert when 40,000 spectators get their first taste of the venue.
"Testing the Olympic Park and its operations is a hugely important part of our plans," said London Games chairman Sebastian Coe.
"Over the last 10 months, over 250,000 spectators have watched world-class sport as part of the London Prepares series test event programme, and, in doing so, every one of them is helping us deliver the best possible Games."
[Two British Royal Air Force Typhoon FGR4 aircraft fly over RAF Waddington via AFP]