The Special Duties Unit (SDU, nicknamed 飛虎隊 "Flying Tigers") is a secretive and elite paramilitary police unit of the Hong Kong Police. It is a sub-division of the Police Tactical Unit (PTU). Its primary function is close quarters counter-terrorism. It is considered to be among the best of such units in the world along with British SAS and German GSG-9 and hold regular training excerises with similar units from around the world.