They are front and centre of the fight against violent crime, but the Met's Territorial Support Group (TSG) is also a key unit in the response to terrorist incidents.
Sky News has been filming for several weeks with 3 area TSG, based in Romford, east London.
Little is ever routine with this elite unit, but today was meant to have been a day of anti-violence patrols in the east London borough of Tower Hamlets.
The unit's officers were preparing to head there when the call came through about a major incident unfolding on London Bridge.
As a convoy of TSG vehicles headed to the scene, regular updates were coming through the officers' radios, indicating events on London Bridge were extremely serious.
Reports of multiple people stabbed – that a suspect may have been shot – and that the danger was far from over.
Many of these TSG officers had responded to the last terrorist attack on London Bridge in 2017.
More from London Bridge Attack 2019
It was an unprecedented year of terrorist activity for them, with five attacks, including four in the capital.
Sergeant Simon Barrell, in charge of our unit, told me the initial reports are always confusing in the early stages of any major incident and that his officers had to be prepared for anything.
These officers are well-trained in dealing with violent suspects and many wear Taser stun guns.
But as always with a marauding terrorist attacker, it is firearms officers who are the preferred teams to deal with such suspects.
Like the London Bridge attack in 2017, it was a City of London police armed response team who confronted and shot dead the attacker this time round.
That unit was on scene within five minutes of the first emergency calls.
Battling through Friday afternoon traffic from the outer reaches of east London, it took TSG officers a little over 20 minutes to reach the scene.
The TSG teams gathered on Eastcheap just yards from the north end of London Bridge, the spot where their armed colleagues had confronted and shot the terror suspect.
Although one attacker had been dealt with, officers didRead More – Source