Like many of its counterparts worldwide, the elite police tactical unit known as the Flying Tigers was established in the aftermath of the 1972 Munich massacre, in which 11 members of the Israeli Olympic team were taken hostage and eventually killed by members of the Palestinian terrorist group Black September.
After the tragedy, governments across the globe, including the British colonial administration, saw the need for special counter-terrorism task forces.
Modelled on Britain's Special Air Service, Hong Kong established the Special Duties Unit in 1974 to conduct counter-terrorism work, hostage rescue and other high-stakes tactical operations. Members are known as the Flying Tigers for their exemplary courage.
The squad has always been something of a mystery to the public, as police have never spoken with the media, or released much information, about it. Squad members are bound by a confidentiality agreement not to reveal their job duties to anyone.
According to the force's official description, the SDU is positioned as a task force to deal with terrorist attacks as well as serious crimes that involve firearms or large-scale hostage taking.
The first generation of the squad used weapons the police force had on hand, but devised their own tactics. In 1978, an appraisal of the unit by the British SAS led to considerable changes in equipment and tactics, according to a past issue of the force's newspaper Offbeat.
Since its founding, the Flying Tigers have maintained an impeccable track record of zero failures in all 162 missions and 335 underwater searches they have conducted. A source with knowledge of the elite squad's training credited its success to strenuous physical and mental preparation.
"All physical training works towards one end," the person said. "It's not only about physical fitness. It is the will to accomplish the mission that matters most."
As part of their training, team members must face uncomfortable situations in order to ensure they're sharp in any conditions and not susceptible to issues like vertigo or claustrophobia.
"It is not uncommon that they would have to stay in a very harsh physical environment for two to three days to wait in ambush, and they are required to be ready for action any minute."
But the squad sees fewer violent operations these days as the nature of crime has shifted. Instead of wielding AK-47s to rob banks and jewellery shops, criminals have moved to cyberspace to make money since the turn of the millennium.
After the 2003 arrest of the city's most wanted man, Kwai Ping-hung, during which they also seized the biggest cache of firearms in nearly 30 years, the squad did not face another gunfight until June. That's when they used stun grenades and tear gas to storm the Kowloon Bay flat of a gunman who allegedly killed a neighbour and later himself.
Two teams from the Special Duties Unit were deployed. One team, comprising more than 20 members, went into action while the other was on standby.
Before the Kai Ching Estate shootout, the last major mission the squad undertook was in 2011, when a haul of 567kg of cocaine, worth an estimated HK$600 million, was seized in Tuen Mun.
Some 383 people have served with the unit over the years. It now includes 100 members and five Belgian shepherd dogs. Applications are open to women officers, but no women are currently in the unit and only one has served. She did mainly administrative work nearly a decade ago.
In 2012, the city established the police Counter Terrorism Response Unit. But the SDU still plays an important anti-terrorism role, according to the force insider. The new unit is mainly tasked with prevention and intelligence gathering, while the Flying Tigers is still indispensable for complex operations that require detailed advance planning.