Up to 13,500 military personnel will help provide security during next summer's Olympics, it was announced today.
The Ministry of Defence said the servicemen and women would be on hand across the UK to protect 150 venues and training sites.
HMS Ocean and HMS Bulwark will also be based at Greenwich and Weymouth bay respectively.
The figure of 13,500 is significantly higher than the 7,000 that had been widely expected.
Some 3,500, rising to a peak of 7,500, will provide venue security.
Around 5,000 servicemen and women will support the police and other civil authorities, providing specialist capabilities such as bomb disposal and dog teams.
Another 1,000 will provide logistical support.
There will also be a 1,000-strong unarmed contingency force for deployment in the event of an "Olympics-related civil emergency".
Typhoon jets will be stationed temporarily at RAF Northolt, and Puma and Lynx helicopters will operate from HMS Ocean.
Defence Secretary Philip Hammond said: "Next year's Olympic and Paralympic Games are once-in-a-generation events for the UK.
"We want them to be secure, so that all those competing and attending can enjoy the Games for the celebration of sporting achievement and cultural celebration that it is."
He added: "The Royal Navy, Army, and Royal Air Force between them will provide up to 13,500 personnel.
"Up to 7,500 of them will support the smooth running of Olympic sites while the remainder will use their specialist capabilities and equipment to contribute to the delivery of Olympic security.
"I have no doubt that they will do a fantastic job - and I look forward to their professionalism and agility being on show on the world stage once again."
The number of security staff required at the Games has risen from an initial estimate of 10,000 to 23,700.
The military is now due to contribute 7,500 of that figure during the 17 days when the event is taking place. The costs are expected to be recouped from the £553million Olympics security budget.
Mr Hammond said: "These numbers will be in addition to the ceremonial role which the armed forces will play during the Olympics, which will showcase our armed forces to the world.
"This defence contribution is on a similar scale to that deployed at other recent Olympic Games and will contribute to ensuring a safe, secure and enjoyable 2012 Olympics."
Mr Hammond stressed that operations in Afghanistan and elsewhere would not be affected by the deployment.
"My priority will remain the troops we have deployed on operations, including in Afghanistan, before, during and after the Olympics."
London mayor Boris Johnson said: "I am delighted that the great men and women of our armed forces will play a part in next year's Games.
"It is only right that they should be involved in this happy and momentous occasion, providing reassurance to everyone who will be celebrating with us in 2012."