Tom Clancy's Rainbow Six Siege is a first-person shooter game, in which players utilize many different operators from the Rainbow team. Different operators have different nationalities, weapons, and gadgets. The game features an asymmetrical structure whereby the teams are not always balanced in their choices of abilities. The base Counter-Terrorism Units (CTUs) available for play are the American Hostage Rescue Team (referred to in-game as the FBI SWAT), the British SAS, the German GSG-9, the Russian Spetsnaz and the French GIGN, each of which has four operators per unit split between attackers and defenders (other units were later added through downloadable content, see below). Players also have access to a "Recruit" operator who can choose from a more flexible assortment of equipment at the expense of having a unique gadget or the ability to customize their weapon. Players can pick any operator from any unit that is defending or attacking before a round starts, choosing spawn points as well as attachments on their guns but are not allowed to change their choices once the round has started.