Operation Green often also referred to as Case Green or Plan Green, was a full-scale operations plan for a Nazi German invasion of Ireland planned by an unknown German officer known by the alias "Hadel" in support of Operation Sea Lion, the invasion of the United Kingdom, during World War II. Despite its detailed nature, Operation Green is thought to have been designed only as a credible threat, a feint, not an actual operation. Plan W, a planned occupation of all of the Free State by the British Armed Forces, was drafted by the British military in secret liaison with the Irish government to counteract any German invasion.

The Emergency was a state of emergency in the independent state of Ireland in the Second World War, throughout which the state remained neutral. It was proclaimed by Dáil Éireann on 2 September 1939, allowing the passage of the Emergency Powers Act 1939 by the Oireachtas the following day. This gave sweeping powers to the government, including internment, censorship of the press and correspondence, and control of the economy. The Emergency Powers Act lapsed on 2 September 1946, although the Emergency was not formally ended until 1976.