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 Blitzkriegs 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. German planning for Operation Green began in May 1940 and the British began intercepting communications about it in June. The British were interested in securing Ireland, as its capture by German forces would expose their western flank and provide a base of operations for the Luftwaffe in the Battle of the Atlantic and in any operations launched to invade Great Britain as part of Operation Sea Lion.

Irish-British co-operation was a controversial proposal for both sides, as most members of the Irish political establishment had been combatants in the Irish War of Independence between 1919 and 1921. However, because of the threat of German occupation and seizure of Ireland and especially the valuable Irish ports, Plan W was developed. Northern Ireland was to serve as the base of a new British Expeditionary Force that would move across the Irish border to repel the invaders from any beach-head established by German paratroopers. In addition, coordinated actions of the Royal Air Force and Royal Navy were planned to repel German air and sea invasion. According to a restricted file prepared by the British Army's "Q" Movements Transport Control in Belfast, the British would not have crossed the border "until invited to do so by the Irish Government," and it is not clear who would have had the operational authority over the British troops invited into the State by Éamon de Valera. The document added that most people in Ireland probably would have helped the British Army, but "there would have been a small disaffected element capable of considerable guerrilla activities against the British."

By April 1941, the new BTNI commander, General Sir Henry Pownall extended his planning for a German invasion to cover fifty percent of the entire Irish coastline. He believed that German troops were likely to land in Cork, Limerick, Waterford, Westport, Galway, Sligo, and County Donegal, i.e. on the southern or western coasts. British Army personnel also carried out secret intelligence-gathering trips to glean information on the rail system south of the border.
Q362
World War II
EVE
Q27
Ireland
LOC
Q145
United Kingdom
LOC
Q7318
Nazi Germany
Concept
Q6071693
officially neutral
Concept
Q56506
Blitzkrieg
Concept
Q153341
Operation Sea Lion
EVE
Q2253432
Operation Green
UNK
Q825712
intercepting communications
MEDIA
Q2564009
Luftwaffe
Concept
Q157627
Battle of the Atlantic
EVE
Q208297
Irish War of Independence
EVE
Q26
Northern Ireland
LOC
Q3277777
British Expeditionary Force
MEDIA
Q670200
Irish border
Concept
Q749387
paratrooper
Concept
Q165862
Royal Air Force
Concept
Q172771
Royal Navy
ORG
Q222595
British Army
ORG
Q173347
Éamon de Valera
PER
Q720396
Henry Pownall
PER
Q162475
Cork
LOC
Q133315
Limerick
LOC
Q183551
Waterford
LOC
Q1017331
Westport
LOC
Q129610
Galway
LOC
Q190002
Sligo
LOC
Q179424
County Donegal
LOC
Q7200911
Plan W
PER
Q7200911
Plan W
PER
1940-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1940
DATE
1942-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1942
DATE
1939-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1939
DATE
1940-05-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
May 1940
DATE
1919-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1919
DATE
1921-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1921
DATE
1941-04-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
April 1941
DATE
+40^^http://www.w3.org/2001/XMLSchema#decimal
40
NUMBER
part of
diplomatic relation
participant