On 13 December 1941, a Royal Navy convoy comprising the battleship HMS Duke of York and three destroyers set sail for America from the River Clyde.

The Duke of York was taking UK prime minister Winston Churchill on a tryst with destiny in Washington and a conference with US president Roosevelt.

America had been Britain’s co-belligerent (though not yet an ally) since Japan’s attack on Pearl Harbour less than a week earlier and the declaration of war against the US by Germany and Italy on 11 December.

Britain was now in partnership with both the US and the Soviet Union, which had been invaded by Axis armies in June.

There were other encouraging developments. In the Western Desert, British, Commonwealth and Imperial forces had made impressive advances in Operation Crusader. The previous month, it relieved Tobruk which had been under siege for seven months.

News from Asia was worrying. Hong Kong was under attack and would fall on Christmas Day. This set the scene for a disaster in Malaya, Singapore and Burma in 1942.

But Churchill was travelling in hope. He knew Britain couldn’t be beaten. His objective was to agree with the US how it could eventually win.

What he and Roosevelt decided in the winter of 1941was to change the course of the Second World War and seal the fate of the men who would soon become the Irish Brigade.

Churchill’s convoy arrived in Washington on 22 December and the conference, named Arcadia, immediately began.

His advisers included Admiral of the Fleet, Sir Dudley Pound;  Field Marshal Sir John Dill (who was Chief of the Imperial General Staff); Chief of Air Staff Charles Portal  and  Air Marshal Arthur Harris. Roosevelt’s key adviser was General George Marshall, chief of the staff of the US Army.

Arcadia was the first major international conference of the Second World War. A total of 24 nations participated but it was dominated by what was known as the Big Four: China, the Soviet Union, the UK and the US.

Other participants were the Commonwealth states of Australia, Canada, India, New Zealand and South Africa and the representatives of occupied countries: Belgium, Czechoslovakia, Greece, Luxembourg, the Netherlands, Norway, Poland and Yugoslavia. Nine Caribbean and central American countries were also involved. France, which had signed an armistice with the Third Reich in June 1940, wasn’t.

Arcadia had two main purposes. The first was to establish a system for American and British chiefs of staff to co-operate.

The second was to agree where allied attacks should take place.

Arcadia quickly confirmed that defeating Axis powers in Europe – not defeating the Empire of Japan — would be the first objective. On 23 December, Churchill proposed that US forces should land in French Morocco. Dismissing advice from Marshall that the Pacific should be America’s priority, Roosevelt agreed.

The commitment to Europe first was tested during the conference by the deteriorating position of British and US forces in the Pacific. But it was reaffirmed by the time the conference closed.

The Anglo-American expedition to French North Africa approved at Arcadia and named operation Torch began on 8 November.

A new world order that would prevent future conflicts was agreed. The founding declaration of the United Nations was drafted at the White House on 29 December by Roosevelt, Churchill and Roosevelt’s adviser Harry Hopkins. It was signed by 26 countries on 1 January 1942, setting the scene for the establishment of the UN Organisation in 1945.

The conference closed on 14 January and Churchill returned to the UK.

Two days earlier, the 38 (Irish) Brigade had been formed to fulfill Churchill’s request the previous November. On 17 January, the first members of the brigade started to assemble in a depot in Norfolk.

Ten months later, the brigade set sail, like Churchill in December 1941, on its own fateful journey. Its destination was French North Africa to join the campaign agreed when Churchill met Roosevelt in Washington.