What's behind London's decision to add more armed police officers?

London is known for having unarmed police officers on its streets. But more "bobbies" are about to have guns on them.

Police Commissioner Bernard Hogan-Howe announced on Thursday that 600 more armed police officers will be trained and put on the streets, increasing the number to 2,800. The number of armed response vehicles will also be doubled.

The move is an effort to increase the ability of police officers to respond to sudden attacks, such as the terrorist attacks in Paris that left 130 dead last November. Following Paris, Hogan-Howe said that London is likely to face a “spontaneous attack that requires a fast response."

“The tragic attacks in Paris reinforced the vital role that firearms officers would be called upon to play on behalf of all of us, to run forward and confront the deadly threat that such attackers would pose," Hogan-Howe said in a statement. "Whilst I sincerely hope it is something that never happens on our streets, it is only right that the Met are as ready as can be.”

But many police officers remain uncertain about when to use firearms, according to the BBC. Britain’s Criminal Law Act 1967 allows police officers to use “reasonable force,” but police officers often come under close scrutiny when they are involved in a shooting.

A police officer involved in the fatal shooting of Jermaine Baker last month, in north London, was arrested, and later suspended for the incident. The Independent Police Complaints Commission launched a homicide inquiry on the officer, raising concerns regarding the use of arms by police officers.

“When somebody is shot dead, of course the police have to account for what has happened, but some of these cases take five, seven, 10 years to resolve. That's completely absurd," former Met Police commissioner Lord Blair told Sky News. "These are men and women who go to work to do an incredibly dangerous job for which they volunteer and if they do their duty and shoot somebody because they have to.... [T]hey should not be treated as criminals."

Last December, Hogan-Howe raised concerns that officers were probed unfairly, and prompted Prime Minister David Cameron to order a review on the police use of firearms, to determine whether officers have enough legal backing in situations where officers have to make "split-second" decision to shoot.

Hogan-Howe has said that the training of the additional 600 officers will not change the "fundamental principle" that the police are routinely unarmed as 92 percent of officers will remained unarmed.

As for Londoners, many had similar reactions

"It actually makes you feel a bit nervous.... it makes you think 'is there something going on?,” Marley Brenner, a Hertfordshire resident, said to the BBC.

"It's not an effective deterrent in stopping anyone, and makes no difference to actual safety. They are never going to use [the guns]," Tom Connolly, a lawyer from Derby, said.