A firearms unit is an armed unit within each territorial police force in the United Kingdom. For the most part, the police forces of the United Kingdom are unarmed; however, all have firearms units to provide the police force with the capability to deal with terrorists and armed criminals. A police officer cannot apply to join the firearms unit without first finishing their two-year probationary period, with a further two years in a core policing role for some forces. Firearms unit is the most common name outside of the capital, while that of London's Metropolitan Police Service is called the Specialist Firearms Command, Trojan or SC&O19. Within the media it is sometimes compared to the SWAT units of the United States.