Armed officers will be patrolling the streets as part of a new task force set up to tackle a spate of fatal shootings in south London.
Billy Cox was shot in the chest
The move, announced by Met Police Commissioner Sir Ian Blair, follows the killing of Billy Cox, 15, in his home in Clapham North, on Wednesday.
He was the third teenager to have been shot dead in south London in the past two weeks.
He was discovered by his 12-year-old sister when she came home from school.
She had returned with a school friend when they heard a bang - shortly afterwards they found Billy who had been shot.
Her friend tried to administer first aid and emergency services were called.
Paramedics tried to resuscitate Billy but he was pronounced dead at the scene.
Officers at the scene said the back door of the house was open and there was no sign of forced entry.
Police confirmed that Billy was electronically tagged after he was served a supervision order that started in December.
Detectives said it was too early in the inquiry for the police to be discussing whether Billy was involved in drugs.
On 6 February, 15-year-old Michael Dosunmu was shot dead in the bedroom of his Peckham home. A man has been arrested in connection with the killing.
Three days earlier, 16-year-old James Andre Smartt-Ford died after he was shot at Streatham Ice Arena.
Sir Ian Blair met senior officers from the Met's Specialist Crime Directorate to discuss the recent shootings on Thursday morning before announcing the new task force.
A lack of role models is an issue for some young victims say the police
It will run alongside Operation Trident, which investigates gun crime in London's Afro-Caribbean community.
Sir Ian Blair said his force was "absolutely determined" to stop the situation escalating any further.
He said gun crime in London had fallen by 14% in the past year, but he admitted this was "no comfort to the families involved in the five murders".
The other two murder victims are Javarie Crighton, 21, stabbed to death in Southampton Way, Peckham on 3 February, and Chamberlain Igwemba, 47, shot in nearby Clayton Road less than 24 hours later.
"There was no evidence that all of these crimes are linked," Sir Ian said.
But he added: "There are some evidential leads that link some of them.
"What they are is entirely unacceptable to the communities of London."
He added that a "new trend" was emerging of teenagers being involved in killings and serious violent crime.
A number of factors were behind it, he said, only some of which were to do with policing.
The lack of role models in some households is an issue, he admitted. "Some of these young people have got very little connection to stable community lives," he added.
Sir Ian said there was a growing recognition in the force about the proportion of young people now involved in serious crime.
Sir Ian has also suggested to the home secretary that the age limit for the five year mandatory sentence for carrying guns should be lowered from 21 to 17.
He said the home secretary "agreed to look at it sympathetically".
1. 14 Feb: Billy Cox, 15, shot dead at his home
2. 6 Feb: Michael Dosunmu, 15, shot dead at his home
3. 3 Feb: James Andre Smartt-Ford, 16, dies after being shot at the Streatham Ice Arena