On Christmas Eve 1914, Capt Arthur O’Sullivan, from Greystones, Co Wicklow, was in his trench at Rue du Bois, near Neuve Chapelle on the western front, when he heard a foreign accent shouting from the opposite side of no man’s land.

“Do not shoot after 12 o’clock and we will not do so either,” said a German voice. A little later, the voice called out again: “If you English come out and talk to us, we won’t fire.”

Thus began the now famous Christmas truce for Arthur Moore O’Sullivan, a 36-year-old career soldier in the British army’s Royal Irish Rifles. Amos, as he was known to his men, played a small but not insignificant role in the playing out of the truce on his part of the frontline trench, section E, not far from where the Italian artist Fortunino Matania would set his painting, The Last General Absolution of the Munster Fusiliers at Rue du Bois, now sadly lost.

What did Amos and his comrades think on hearing the Christmas Eve invitation? Thanks to a memoir by Amos’s commanding officer, Col George Laurie, and the record of his exchanges with brigade headquarters, we know what happened next.

In response to the German invitation, an Irish rifleman ventured out into no man’s land and was not fired upon. Instead, when he reached the other side, he was given a cigar by a German soldier. When he returned safely, other riflemen clambered out of the trench, the Germans now meeting them halfway across no man’s land.

Col Laurie was thrilled with the pause in hostilities. “You have no idea how pleasant everything seems with no rifle bullets or shells flying about,” he wrote later.

His more senior officers were, however, perplexed. Brigade HQ cabled him: “It is thought possible that enemy may be contemplating an attack during Xmas or New Year. Special vigilance will be maintained during this period.”

Nonetheless, Col Laurie, who was with Amos in the trench, gave orders not to fire on the enemy the following day, unless they fired first. At 8.30pm on Christmas Eve, he signalled brigade HQ: “Germans have illuminated their trenches, are singing songs and are wishing us a Happy Xmas. Compliments are being exchanged but am nevertheless taking all military precautions.” No shots had been fired since 8pm, he added.

Col Laurie went on to describe how soldiers from both sides were mingling. The Germans, he wrote, were “fine men, clean and well clothed. They gave us a cap and helmet badge and a box of cigars. One of them states the war would be over in three weeks as they had defeated Russia!”

Brigade HQ replied at 12.35am – Christmas Day – saying: “No communication of any sort is to be held with the enemy, nor is he to be allowed to approach our trenches under penalty of fire being opened.”

There was a hard frost that night, dawn being broken by shouts of “merry Christmas” from the German trenches and, at 8.40am, another missive from brigade HQ: “As long as Germans do not snipe, there should be no sniping from our lines today, but greatest vigilance must be maintained, as Germans are not to be trusted. Our guns will not be firing today unless asked to do so by infantry or unless German guns fire.”

No one did fire and Col Laurie reported at 11.30am on Christmas Day that “all [is] very quiet along my front . . . situation seems evolving into a kind of mutual armistice ending at 12 midnight tonight”.

For the rest of the day, everyone relaxed, German soldiers occasionally jumping up into no man’s land, cheering, dancing and shouting “merry Christmas”.

The regiment’s war diary, a compilation, essentially, of intelligence reports from the battlefield, records the situation as follows:

1 The truce is sought entirely by the enemy.

2 The enemy have asked for two days of this, which has been refused by the officers of the battalion in the firing line.

3 The mutual arrangement is that if either side construct works, or carry out repairs to works, that the other consider not playing the game, they will fire shots over the other side’s heads.

4 Capt O’Sullivan, commanding B Company of the battalion, will fire his revolver at 12 midnight tonight (25th/26th), at which signal the truce ends.

Col Laurie wrote: “Only a few shots were fired by the enemy after the midnight signal was fired by Capt O’Sullivan from our trenches. Shortly after midnight a party of Germans came over towards B Company’s trenches and were ordered back. During the morning of the 26th, the enemy fired very few shots.”

Hostilities resumed gradually and the murderous stagnation of the western front took hold again in the early days of 1915.

In March, O’Sullivan was wounded by German machine-gun fire while trying to cut through barbed wire across no man’s land. This prompted a complementary mention of him in a dispatch by the British commander, Field Marshal Sir John French.

Two months later, Amos was among those who died at the Battle of Aubers Ridge, the same battle that did for so many of the absolved Munsters in the painting by Fortunino Matania.

Just before dawn on the morning of battle, May 9th, 1915, his 1st Royal Irish Rifles moved out of their trench and into no man’s land, from where they could see German bayonets glistening in the dawn sun.

Within a few hours, some 11,500 men had died in a battle that, for the Allies, saw no ground gained nor tactical advantage achieved. One of the German soldiers to survive that battle was, sadly, a certain Cpl Adolf Hitler.

Arthur O’Sullivan was an only son. His father, Patrick O’Sullivan, was advocate general in Madras, India, but died, aged 52, in 1887.

Arthur was born in Tamil Nadu in 1879, but by the time of the war, his mother, Sydney Jane O’Sullivan, a daughter of Dublin doctor and pharmacist William Daniel Moore, was living in the Burnaby Road house in Greystones.

Arthur left £3,208, five shillings and 10 pence to his sister Katherine. She died, apparently of a heart attack, while playing tennis in 1916, and so his estate passed to his other sister, Muriel. He had no children.

He is buried in the Royal Irish Rifles graveyard at Laventie in Pas de Calais, not far from the Rue du Bois.