Continuity of government (COG) is the principle of establishing defined procedures that allow a government to continue its essential operations in case of a catastrophic event such as nuclear war. COG was developed by the British government before and during World War II to counter threats, such as that of the Luftwaffe bombing during the Battle of Britain. The need for continuity of government plans gained new urgency with nuclear proliferation. During and after the Cold War countries developed such plans to avoid (or minimize) confusion and disorder due to a power vacuum in the aftermath of a nuclear attack. In the US, COG is no longer limited to nuclear emergencies; the Continuity of Operations Plan was activated following the September 11 attacks. Canada built numerous nuclear bunkers across the country, nicknamed "Diefenbunkers" in a play on the last name of then-Prime Minister John Diefenbaker. In 2016, the Privy Council Office made an agreement with the Department of National Defence to open two bunkers for government officials amid the ongoing North Korean nuclear crisis. 816 Nuclear Military Plant The People's Republic of China (PRC) once operated Underground Project 131, intended to be the PLA headquarters in Hubei during a nuclear conflict. Built due to the Sino-Soviet split during that portion of the Cold War, in 1981, the Project 131 site was turned over to the civilian authorities of the prefecture-level city of Xianning, where it is located. The K-116 facility under Zlíchov hill in western Prague was designated to house the Czechoslovak government in case of nuclear attack (together with the K-9 facility in Jihlava) and might still be used as the emergency headquarters of the Czech government and military. During the Cold War, Denmark built two bunker complexes, named REGAN Vest and REGAN Øst (Danish: "REGeringsANlæg", translated: "Government Complex West and Government Complex East"), in Jutland and Zealand respectively.