'Blue Thunder': The elite SAS unit deployed to London Bridge
The 70-strong Special Forces squad arrived by unmarked helicopter - nicknamed 'Blue Thunder' - after the alarm was raised, and assisted police in hunting down the attackers.
They were dispatched on the direct orders of the Home Secretary.
The unit was formed in 2015 specifically in response to the feared terrorist threat from rampaging jihadis and 'lone wolf' attackers, and they rehearse such scenarios regularly.
This is the first time they have been deployed on the streets of the UK.
News of the squad's formation emerged after the Brussels terror attacks, and they are now on standby around the clock. Their deployments are supported by an Apache gunship helicopter.