'Plan W' (i) was a British and Irish unrequired plan to defeat any German invasion of Ireland (mid-1940/1942).

Talks about a possible German invasion of Ireland, which was an independent British dominion until 1949, had started in the UK in the first months of 1939, and by June 1940 the British political and military leadership had ample evidence of the capabilities of German aggression in the form of the German defeats of Poland, Denmark, Norway, the Netherlands, Belgium and France. The British rightly suspected that the German were drafting plans for the 'Seelöwe' invasion of the UK, and also suspected that there was a comparable ambition in the direction of Ireland as 'Grün' (iv). In this context, therefore, the British decided on the controversial process of joint planning, with the Irish authorities, for the defence of the whole of Ireland.

Given the nature of the German conquest of Belgium and the Netherlands, the British were convinced that an invasion of Ireland would start with an airborne operation, and were not confident of the Irish defence capability, particularly against the type of operation which would start with an airborne assault. The topic of reoccupying the 26 counties of Ireland had been a matter of British political conversation, and in June 1940 Malcolm MacDonald, the British minister of health, suggested that the UK offer to 'give back' the six counties comprising Northern Ireland and thus allow the creation of a unified Ireland, in return for an Irish adherence to the Allied cause.

In the same month Major General B. L. Montgomery was busy planning the seizure of what he referred to as 'Cork and Queenstown (Cobh) in southern Ireland' to provide a naval base best sited for anti-submarine and convoy escort operations in the South-Western Approaches and eastern Atlantic to offset the advantages the Germans had obtained by their ability to operate from bases on the western coast of France. Attempts were also made on 26 June 1940 to split the consensus in Ireland over the neutrality policy via a possible coup d'état: an approach was made to Richard Mulcahy, leader of the Fine Gael party, by an Irish ex-British army officer then a city councillor in Ireland. 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. He wanted someone to go up there from here unofficially, to speak to someone in authority and say how the land lay. In reply to questioning, he stated that the people he referred to were the British Army authorities in the North.' This was in effect a proposal for a joint military command of Ireland and Northern Ireland, which the unidentified ex-British officer said had been stimulated after discussion with 'important members of the British Army in the North of Ireland'.

It is possible that the simultaneous discussions could have been an attempt to exert pressure on Éamon de Valera, the prime minister of Ireland. The 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. Herdman appears to have been acting on behalf of Lord Craigavon, the prime minister of Northern Ireland, but when de Valera rebuffed him, he was of the view that 'the only thing to do now for Britain is to send in powerful forces here, and prevent this country being seized, or prevent them [the British] having to use and lose large numbers of troops in putting the Germans out if they got here.'

'Plan W' (i) therefore had the twin purposes of creating a joint plan of action in the event of a compliant Ireland, and an invasion plan in the event of an invasion and subsequent resistance from de Valera.

The German planning for 'Grün' (iv) began in May 1940, and the British began to intercept signals about the operation from about the following month. The British were interested in securing Ireland as its capture by the Germans would expose the western flank of the UK and also provide a base of operations for German aircraft and U-boats in the Battle of the Atlantic and in any operations launched to conquer the UK as part of 'Seelöwe'. The British suspected that the primary target for any German invasion would be Cork, an in particular Cork harbour with the naval base at Cobh because it was the nearest to German air bases in north-western France.

The first meeting by British and Irish officials on establishing a joint action plan took place on 24 May 1940 in London, and had been conceived as a means of exploring every way in which the German forces might try an invasion of Ireland. At the meeting were Joseph Walshe, the Irish Secretary of External Affairs, Colonel Liam Archer of Irish Military Intelligence, and officers of the British army, navy and air force. The British War Office wanted direct liaisons between the Irish military authorities in Dublin and the senior British officer in Belfast. Walshe and Archer therefore agreed to fly in secret to Belfast with Lieutenant Colonel Dudley W. Clarke. In Belfast, two British army staff officers were collected and the group travelled back to Dublin by rail. This meeting was held underneath the government buildings in Kildare Street and included a number of Irish army officers. The meeting was informed that Major General Sir Hubert Huddleston, the British commander in Northern Ireland, was already under orders to take a mobile column south of the border to support the Irish army in the event of a German invasion.

Clarke also met with the Irish army chief-of-staff, Lieutenant General Daniel McKenna, who explained that the British would not be allowed into Ireland before any German arrival. 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'.

The point of these meetings was to secure an understanding on the threat faced by both the UK and Ireland, and the benefit of joint action whose details would be worked out later by the respective armed services. Clarke returned to London on 28 May and reported that the Irish army had given him full details of their organisation and equipment 'without reservation', and had in return requested information on British troop strength in Northern Ireland. It had been agreed that in the event of a German invasion, the Irish would call for assistance from Huddleston in Belfast.

The British army’s advance from Northern Ireland into neutral Ireland was 'Plan W' (i). As noted above, Cork was seen as the most likely place for the launch of any German invasion because it was the nearest landfall in Ireland from the German bases in north-western France. Northern Ireland was to serve as the base of a new British expeditionary force which would move into Ireland to help repel the invaders from any beach-head which was established. Troops of Major General B. T. Wilson’s British 53^rd Division in Belfast were held in readiness for the advance. Royal Marine units at Milford Haven in western Wales were also prepared to seize a beach-head in Ireland the moment the Germans landed.

Officers at the headquarters of the British forces in Northern Ireland estimated that the Germans could embark five divisions by sea to Ireland although 'not more than 2 to 3 would reach land'. Up to 8,000 German airborne troops could be flown into Ireland, some of them in seaplanes which would land on lakes.

The British striking force, centred on the 53^rd Division later augmented by the 5/Cheshire Regiment, was to concentrate to the west of the Down and Armagh borders, then drive across the border and head straight to Dublin along three main roads: the coastal road between Belfast and Dublin via Dundalk, Drogheda and Balbriggan, the inland road through Ardee and Slane, and the road linking Castleblaney and Navan via Carrickmacross. It not clear who would have had the operational authority over the British troops invited into Ireland by de Valera, but it is assumed the British would have retained command.

By December 1940 the plan had been extended. While the first British striking force headed for Dublin, Major General A. Carton de Wiart’s British 61^st Division, in a separate undertaking, would move across the border into County Donegal and secure the port of Lough Swilly for the Royal Navy, providing the British government with a third of the naval defence requirements that they had been requesting from de Valera for more than a year. (After the Irish Free State had won independence from the UK in 1922, three deep-water treaty ports at Berehaven, Queenstown [renamed Cobh] and Lough Swilly, were retained by the UK as sovereign bases as a condition of the Anglo-Irish Treaty of 6 December 1921. The existence of the ports was one of the causes of the Irish Civil War, where those who regarded the treaty as a betrayal of Irish Republicanism fought against the forces of the nascent Free State. The ports remained under the control of the UK until the Anglo-Irish Free Trade Agreement in 1938, when they were returned to Ireland. From an Irish point of view, the handover of the ports in the lead-up to World War II was felt to be vital to consolidate Ireland’s neutrality during 'The Emergency'.)

The British Troops in Northern Ireland war diary of the time lists 278 Irish troops at Lough Swilly and only 976 Irish troops in the rest of Donegal. Thus there is some indication that the British were prepared to take advantage of a German invasion, when Irish troops would be fending off attack, to retake the treaty ports. They may also have been prepared to act if they felt de Valera was slow in asking for intervention. The diary goes on to say that in the event of an invasion 'close cooperation is to be maintained with Éire forces including the Local Security Force if friendly'. Why the Local Security Force, an auxiliary service raised for internal security purposes, should not be friendly is not explained although it is known that the British considered invading Ireland without consulting de Valera.

According to a file prepared by the British army in Belfast, the British would not have crossed the border 'until invited to do so by the Éire Government', but added that although most people in Ireland would probably help the British army, 'there would have been a small disaffected element capable of considerable guerrilla activities against us.' Sir John Loader Maffey, the British representative to Ireland since 1939, was to transmit the code word 'Pumpkins' (later replaced by 'Measure') to trigger the movement of the 53^rd Division onto Irish soil. This codeword would be received by Huddleston and Major General H. E. Franklyn, commanding the British troops in Northern Ireland.

Elaborate plans were made in Belfast to supply the expeditionary force with guns, ammunition, petrol and medical equipment by rail. The British marshalling yards at Balmoral, to the south of Belfast, were extended to take long ammunition and fuel trains which, were loaded and ready on new sidings. In addition three ambulance trains were equipped and positioned around Belfast and an ambulance railhead established to take the wounded returning from the south of Ireland. British soldiers stripped the sides from dozens of coal trucks, so transforming them into flat cars for the tanks and other armoured vehicles which would be sent south.

Once the British 53^rd Division was committed in Ireland, the British military authorities planned to run 38 supply trains on the two railway lines to Dublin every day: 30 of them down the main line through Drogheda if the viaduct over the Boyne river remained undamaged, and eight along the track through County Cavan. The port of Belfast was estimated to have to handle 10,000 tons of stores a week and could receive up to 5,000 troops every day for onward transmission to the front.

The RAF was to fly three squadrons of Hawker Hurricane fighters into Baldonnel airfield to the south-west of Dublin and two squadrons of Fairy Battle light bombers into Collinstown to attack the German troops in Cork. The British 1^st Heavy Anti-Aircraft Regiment was to be moved into Ireland to defend the Drogheda viaduct, Collinstown and Baldonnel.

The Royal Navy was to issue instructions that all British and foreign ships should leave Irish ports. Any vessels in Londonderry were to head for the Clyde river and ships in Belfast were to head for Holyhead and Liverpool. As many ships as possible would be cleared from Irish ports and taken to the Clyde, Holyhead and Fishguard. British naval officers in Dublin were to direct this exodus and the evacuation of refugees was not to be encouraged. British submarines were to patrol off Cork and the estuary of the Shannon river 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 southern and western coasts of Ireland.

By April 1941, the new commander of the British troops in Northern Ireland, Lieutenant General Sir Henry Pownall, had extended his planning for a German invasion to cover some 50% of the entire Irish coast. Pownall believed that German troops were likely to land in Cork, Limerick, Waterford, Westport, Galway, Sligo and Donegal. British army personnel also carried out secret intelligence-gathering trips to glean information on the rail system south of the border.

By May 1940 Irish troops were already organised in mobile columns to deal with airborne landings. Working on the assumption that the Germans were going to land where the British and Irish expected them to do so, they would have been engaged by Major General Michael Joe Costello’s Irish 1^st Division from Cork, supported by Major General Hugo MacNeill’s Irish 2^nd Division. The British would establish their railhead near the Fairyhouse race course and be given billets at Lusk, Howth and Portmarnock north of Dublin.

By October 1940 four more regular army brigades had been raised in Ireland, and Local Security Force recruiting figures were increasing. The German-style helmets of the army had been replaced by the pale green uniforms and rimmed helmets of the British army. The Irish army had 16 medium armoured cars and 13 old Rolls-Royce light armoured cars.

The cadre squadron of four Gloster Gladiator biplane fighters of Major P. Mulcahy’s Aer Corps provided the only air defence capability in Ireland. In 1940, however, six second-hand Hawker Hind light bombers were added to the Irish Air Corps, and later in the war the Irish cannibalised and repaired several German and Allied aircraft which had crash-landed in their territory.

Colonel A. Lawlor’s Irish Naval Service acquired its first motor torpedo boat only in January 1940, leading to a total of six by 1942. However, the only patrol vessels were Mirchu and Fort Rannoch, two former British gunboats. Beside these vessels there was one 'mine planter' and one barge. The Irish Naval Service acquired no other vessel during World War II.

Irish preparations for the defence of Ireland included plans for defence against British as well as German attack. For example, in Cork, the Irish 2^nd Division faced to the north, and the Irish Army spent weeks preparing two lines of defence against British invasion, placing explosives beneath bridges along rivers and canals between County Donegal to County Louth. The first line of defence, through Longford and Cavan, was centred on the canal between Ballinamore and Ballyconnell. The second line chosen was the Boyne. After a delaying action and a conventional static defence, the 2^nd Division was to 'split up into smaller groups and start guerrilla resistance against the British'.

In overall terms, the policy of neutrality adopted by the government of de Valera widened the political divide between Ireland and Northern Ireland, and led to the frequent charge that the Irish had shirked their responsibilities in World War II. From this point of view it can be seen that Irish neutrality reinforced the identity the Unionists of Northern Ireland sought with the UK.