Typhoon jets and the largest ship in the Royal Navy's fleet will be deployed to protect the London 2012 Games along with up to 13,500 military personnel, the Ministry of Defence has said.
Original estimates that a 10,000-strong security force would be needed have dramatically increased to 23,700 after an in-depth venue-to-venue analysis of the scale of the job.
The 13,500 deployment across all the military services is significantly higher than the 7,000 that had been widely expected.
Defence Secretary Philip 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," he added.
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, and 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 HMS Ocean.
Earlier estimates had suggested that around 10,000 security guards would be required within 150 Olympic venues and training centres during the Games, costing £282 million. The costs are expected to be recouped from the £553 million Olympics security budget.
Dr Tobias Feakin, director of national security and resilience at the Royal United Services Institute, said: "There is a lot of strain on military capacity already and, in that regard, having to supply additional forces for the Games is another strain but it is one that the military will take on board. If they are given a task, they will do it."