Plan W
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. Although Ireland was officially neutral, after the German invasions of 1939–40 that resulted in the defeat of Poland, the Low Countries and France, the British recognised that Germany planned an invasion of Britain (Operation Sea Lion) and were also concerned about the possibility of a German invasion of Ireland.