Plan W

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.

"[3] By April 1941 the new British Troops in Northern Ireland (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.

In June 1940, Britain's political and military establishment had witnessed the seemingly invincible German Blitzkrieg which led to the defeat of Poland, the Low Countries, and France, and the retreat of the British Expeditionary Force from Dunkirk.

The same month Major General Bernard "Monty" Montgomery was busy planning the seizure[5] of what he referred to as "Cork and Queenstown (Cobh) in Southern Ireland" (sic).

Winston Churchill was to also refer to the "... most heavy and grievous burden placed upon Britain by the Royal Navy's exclusion from the three Treaty Ports [in Ireland].

An approach was made to Richard Mulcahy (leader of Fine Gael at the time) by an Irish-born ex-British Army lieutenant colonel who was a city councillor in the State.

Mulcahy recorded that the ex-officer: "...called to say that 'the people in the North are prepared to make a military convention with this country [Ireland] without reference to the Northern Government...

Unionist politician Sir Emerson Herdman also called to speak with de Valera about obtaining "unity of command" and to ask if Ireland would enter the war in return for an end to partition.

In Cork city, any seaborne invaders would be engaged by motor torpedo boats and the 9.2 inch and six-inch guns of the Treaty Ports.

Northern Ireland, was already under orders to take a mobile column south of the border to help the Irish Army if the Germans invaded.

[12] Clarke also met with the Irish Army Chief of Staff, General Daniel McKenna, who explained that the British would not be allowed into the south of Ireland before the Germans arrived.

Clarke also met with the Irish Minister for Co-ordination of Defensive Measures, Frank Aiken, and discussed "new ideas for the mechanical improvement of the war.

"[13] The point of these meetings was to secure an understanding on the threat faced by both Britain and Ireland, and the benefit of joint action – the details would later be worked out by the respective armed services.

Northern Ireland was to serve as the base of a new British Expeditionary Force, that would move into the State to repel the invaders from any beach-head that was established.

A brigade of Royal Marines stationed at Milford Haven were also prepared to seize a bridge-head in Wexford the moment the Germans landed.

It is a feature of other British documents from the time; for example one reads "If Éire be hostile it may be necessary for Royal Signals units to take over the civil telephone system".

"[3] Sir John Loader Maffey, the British representative to Ireland since 1939, was to transmit the code word "Pumpkins" (later replaced by "Measure") to begin the troop movement of the 53rd Division onto Irish soil.

The British marshalling yards at Balmoral, south of Belfast, were extended to take long ammunition and fuel trains which were loaded and ready on new sidings.

British soldiers stripped the sides from dozens of coal trucks transforming them into flat cars for armoured vehicles and tanks that would be sent southwards.

British submarines were to patrol off Cork and the Shannon in readiness for an invasion, and should one occur, the Royal Navy was to declare a "sink on sight" zone in the western approaches and off the south and west coasts of Ireland.

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.

British Army personnel also carried out secret intelligence gathering trips to glean information on the rail system south of the border.

The Irish Air Corps consisted largely of nine Avro Anson light bombers and four Gloster Gladiators, which provided the only fighter defence for the country.

However, in 1940 six second-hand Hawker Hinds were added to the Air Corps and later in the war the Irish cannibalised and repaired several Allied aircraft that had crash landed in their territory, eventually putting two RAF Hurricanes, a Fairey Battle and an American-built Lockheed Hudson into service.