The deployment takes the extra troops brought in for the Olympics to 4,700
Britain has drafted in another 1,200 troops to plug a security gap at the London Olympics left by the failure of a private security firm to provide enough guards.
The deployment announced Tuesday, just three days before the opening ceremony, takes the extra troops brought in for the Olympics to 4,700, after security giant G4S said it could not provide the 10,000 guards it had originally promised.
Culture Secretary Jeremy Hunt said the numbers to be provided by G4S "continue to rise significantly" but that ministers would "leave nothing to chance" in Britain's biggest ever peacetime security operation.
In total, 18,200 soldiers are now helping to guard 10,500 competitors at the Games, alongside thousands of private guards and police.
Meanwhile, the London organisers were struggling to keep secret the details of the opening ceremony overseen by "Slumdog Millionaire" director Danny Boyle after spectators at a rehearsal leaked images and details through social media.
Tens of thousands of people attended a technical rehearsal on Monday, one of the final run-throughs before Friday's £27 million ($42 million, 34.5 million euro) spectacular.
Boyle pleaded with the audience, which included guests of the Games organisers and family of those taking part, not to leak details about the event.
The Twitter hashtag "savethesurprise" was emblazoned on the stadium's giant screens.
Boyle and his creative team have done their best to keep most details of the opening ceremony secret.
Organisers have already revealed that the show features an idyllic British scene including live animals, as well as a tribute to the state-run National Health Service, reportedly involving giant hospital beds.
The security issue continues to dog the Games, but Paul Deighton, the chief executive of London Games organisers LOCOG, insisted the decision to deploy the additional troops was simply a case of "changing the mix within the existing (security) plan".
"You can't be absolutely certain of anything with a temporary workforce," Deighton told journalists.
"Therefore we want to substitute a temporary workforce with a permanent, reliable workforce that we get with the military."
The killing of 11 Israelis at the 1972 Munich Olympics in a massacre by Palestinian guerrillas has haunted every Games organisers since.
On Tuesday, the widow of one of the victims branded Olympic officials "chickens and cowards" for refusing to hold a minute's silence at the opening ceremony in London.
Ankie Spitzer, whose fencing coach husband Andre was among those who died, was to deliver a petition of 103,000 signatures to International Olympic Committee president Jacques Rogge on Tuesday.
The Olympics chief has refused to commemorate the dead during the opening ceremony, although he held an unplanned minute's silence when he toured the London Athletes' Village on Monday.
Spitzer accused Rogge of hiding behind half-hearted "tricks".
"I have told Rogge to make a stand, make history," she said in comments reported in The Times newspaper.
"He told me his hands were tied. I said, 'My husband's hand and feet were tied when he was taken hostage and murdered at the Olympics'. He does not have the balls to make a stand."
It was later revealed that Games organiser Sebastian Coe will run to become the next president of the International Association of Athletics Federations (IAAF).
The double gold medalist, now chairman of the London Olympic Organising Committee, told the Times newspaper he wanted to take over the presidency after elections in 2015.
"I'd be happy to run my sport and that is the first time I've given that answer," he said. "I'm ready. I know how to do this. But we have a great president in the post, so it would be when he stands down."