SWAT teams — or their equivalent — exist in Police forces all over the world and are used to perform high-risk operations beyond the capabilities of regular officers such as hostage rescue, armed intervention and counter-terrorism.

The first Special Weapons and Tactics Team was established in Los Angeles in 1967 and many American police departments, especially in major cities, have similar elite units. The UK equivalent is the Specialist Firearms Command or CO19 in the Metropolitan Police in London.

SWAT teams are usually equipped with specialised firearms including assault rifles, submachine guns, shotguns, carbines, riot control agents, stun grenades and high-powered rifles for snipers.

They might also use trained dogs, stun and tear gas grenades, battering rams, explosive charges and pepper spray. Other equipment could include heavy body armour, entry tools, armoured vehicles, advanced night vision optics and motion detectors for determining the positions of hostages or hostage takers inside an enclosed structure.

Officers in such units usually wear distinctive jumpsuits or battle dress uniforms with armoured vests able to carry ammunition and specialist gear, such as binoculars and fibre optic cameras.

Depending upon the situation they find themselves in, they might wear tactical gloves, a balaclava or protective face covering, eye goggles, a gas mask and steel reinforced boots.

Units such as the Ohio State Highway Patrol's Special Response Team use a vehicle called a BEAR — a very large armoured truck with a ladder on top to gain entry into the upper floors of buildings.

SWAT duties can include hostage rescue, drug raids, close quarters combat, crime suppression, issuing high-risk warrants and security. It is expensive to train officers and call-outs can be infrequent so SWAT officers are usually deployed to regular duties in between assignments.

Los Angeles Police Department's website states that the need for SWAT expertise and assistance is dependent upon unusual circumstances such as a heavily fortified location, a situation where weapons are present and have been used in the past, a location where gang members are known to be present or a situation where the use of diversionary tactics is anticipated.

LAPD's SWAT team — for a city just under 500 square miles with a population of almost four million — usually gets less than 150 call-outs a year and issues about 120 high-risk warrants.

Its first famous mission was on December 9, 1969, when search warrants for illegal weapons were served at the Black Panther Headquarters.

The Black Panthers resisted and attempted to shoot it out with 40 members of the SWAT team in a four-hour siege, which saw thousands of rounds of ammunition fired.

Three Panthers and three police officers were wounded before the Panthers surrendered.