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.

Plan W, during World War II, was a plan of joint military operations between the governments of Ireland and the United Kingdom devised between 1940 and 1942, to be executed in the event of an invasion of Ireland by Nazi Germany.