Whether or not Finglas man Charlie Brennan was the soldier in that famous rescue scene from the Battle of the Somme documentary (An Irishman’s Diary, September 19th), one thing we definitely do know about the rescuer is that his immediate mission was in vain.

The film notes that the wounded comrade being shouldered through the trenches died half an hour later. Brennan may well have helped save other lives that day: the soldier depicted is said to have carried numerous colleagues in the same manner. But in any case, it is part of Brennan family lore that after Charlie came back to Dublin, post-war, he was to play a part in saving the life of one of his own brothers.

And the circumstances of this event illustrate the transformation of the country that Irish soldiers of the Great War had left in 1914. Not long after Charlie Brennan fought at Gallipoli and the Somme, his teenage brother Francis (also known as “Terry”) joined the IRA. He was locally active during the War of Independence. But by 1922, he was fighting on the Anti-Treaty side in the Civil War, as part of a briefly notorious unit called the “Leixlip Flying Column”.

For several months in late 1922, while the anti-Treaty side in general floundered, the Leixlip column carried out a vigorous campaign against Free State forces and infrastructure in East Kildare, attacking railways lines and bridges, and raiding post offices. In their most daring plan, they infiltrated forces defending Baldonnel Aerodrome, intending to attack and destroy it. Had this succeeded, according to some accounts, they also hoped to fly fighter planes into Dublin and bombard Leinster House, where the Dáil had just taken up residence, although there is some dispute as to how serious that ambition was.

The Baldonnel attack was eventually abandoned, anyway. What the column became best known for instead, on December 1st , 1922, was ambushing a Free State Army lorry at a place called Pikes Bridge, on the Royal Canal near Maynooth. This was to be simultaneously their most dramatic action and their last hurrah.

I’m indebted to Christopher Lee – a historian and Brennan relative – for his account of the event: “The Last Stand of the Leixlip Flying Column”.

It began when the “irregulars” took over a country house and attacked the army lorry, which had broken down near by. After a short gun battle, the three passengers were taken prisoner and the vehicle set on fire.

But then inexplicably, the leader of the column, Patrick Mullaney, did not vacate the area with his prisoners, even as large numbers of National Army reinforcements descended. By the time the columnists did retreat, they were increasingly outnumbered. And after a cross-country battle, lasting hours, it was their turn to surrender.

A Free State soldier had died, and several on both sides were injured. But on behalf of the victors, Commandant General Hugo McNeill is said to have congratulated Mullaney and his men “on a damn good clean fight”. Mullaney would later tell Ernie O’Malley that McNeill had not known how close he was to death. The irregulars at one point “had him cornered with a rifle and tommy gun”, but before they could shoot, “something else happened”.

Clean fight or not, five members of the flying column were duly executed for treason. Wearing National Army uniforms when caught, or otherwise found guilty of desertion, they were shot by firing squad in Portobello Barracks on January 8th.

That month saw no fewer than 34 executions of anti-Treatyites, as the Civil War entered its bitterest phase. And the other members of the flying column, including Francis Brennan, might have gone the same way. But in the event, they escaped with prison sentences.

John Brennan, a grand-nephew of both Charlie and Francis, who is now campaigning to have the former recognised as the man in the Somme film, believes he intervened on Francis’s behalf.

Either way, the younger Brennan survived.

The phrase that summed up Gen McNeill’s close shave – “something else happened” – might also be applied to the plight of Irish soldiers in the British army around then. They had gone off to the war as patriots but came back to an Ireland where heroics in the Allied trenches were not something to shout about. This might help explain why, although everyone in 1916 Finglas seems to have known that Charlie Brennan was the man in the Somme film, it has taken 102 years and counting for officialdom to put his name on the face.