London Bridge Terror Attack
An ARV is seen at the scene of the terror attack on the London BridgeDANIEL SORABJI/AFP/Getty Images

The armed response vehicles or the ARVs were among the first to respond to the emergency calls as terrorists struck on the London Bridge and Borough Market on 3 June.

According to Scotland Yard, "three London attackers were shot dead by police from an armed response vehicle within 8 minutes of first emergency call."

Mark Rowley, Britain's top anti-terrorism officer, said, "Armed response officers then responded very quickly and bravely and confronted the three male suspects who were shot and killed on Borough Market."

Armed Response Vehicle -- adding firepower to British Police

An ARV is a type of police car operated by British law enforcement. ARVs are crewed by Authorised Firearms Officers to respond to incidents believed to involve firearms or other high-risk situations.

British police remain largely unarmed, unlike most of their counterparts across the world. Around 92% of the Met are still unarmed.

ARVs are identifiable by a yellow dot sticker, visible from any angle, and an asterisk on the roof to enable helicopters to identify the vehicle as being an ARV.

The ARVs were introduced to the British Police in 1991. ARVs are usually manned by a three-man crew, which consists of a driver, a communications operator and an observer/navigator. ARV officers usually carry Glock 17 handguns, Heckler & Koch G36C 5.56mm carbines and tasers.

The ARVs patrol around Britain and their numbers were increased across the country after the November 2015 terror attacks in Paris.

Met Police Commissioner Sir Bernard Hogan-Howe had unveiled plans last January to equip 600 more police officers in the capital with guns -- bringing the total number of armed officers to around 2,800. The extra 600 firearms officers cost about £25m of the extra £34m that the Home Office had made available.

Scotland Yard chiefs have refused to reveal the actual number of armed response units on duty because this information could aid terrorists plotting an attack.