The siege is one of the biggest ever operations for Scotland Yard's SO19 tactical firearms group, who are operating from a police tent inside the cordon and dressed in their full body armour and metal helmets. They have access to three types of automatic weapon - Smith and Wesson 9mm revolvers, Glock 9mm self-loading pistols, and high-powered Heckler and Koch 9mm carbine rifles. They also have access to CS canisters.