HMS Ocean, the Royal Navy's biggest ship, is to be moored in the Thames and 13,500 armed forces personnel deployed during next year's Olympic Games.
The extra measures have helped send the security costs of the games spiralling to around £1bn.
Defence Secretary Philip Hammond announced that there would be 7,500 forces personnel dedicated to venue security.
Typhoon jets will be moved to RAF Northolt to provide air cover during the seven weeks of the games.
HMS Bulwark, an amphibious assault ship, will be based in Weymouth. Both craft will carry Puma or Lynx helicopters.
They can also carry the Apache attack helicopter armed with cannon and Hellfire missiles.
Specialist dog handlers, bomb disposal experts and another 1,000 unarmed forces personnel will be asked to support up to 12,000 police and other civil authorities.
Although the Ministry of Defence (MoD) will not comment on Special Forces deployments it is also known that both the Special Air Service and the Special Boat Service will be on standby to react to any terrorist incident, and will be based in secret locations in central London.
Originally the policing and security budget for the Olympics was set at £600m with a £238m contingency fund.
The MoD said it could not give a figure for the costs of the deployment of the equivalent of a brigade to protect the Olympics.
Mr Hammond was keen to note that "support for the games will not divert the MoD from its core business".
His officials stressed that the funding for the military component of the Olympics would not be coming out of the defence ministry budget.
Last week the government announced that an extra £270m was being set aside for Olympic venue security from its total budget of £9.3bn.
This implies that around a quarter of the cost of security for the games was unplanned.
The additional troops will be provided to boost the total number of private and national security personnel to around 23,000.
The original plan had been for just 10,000 private security officers, plus the police.
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."