Files released at the National Archives in Kew, west London, show the men were awarded compensation by the British government in recognition of the horrific conditions they endured at the hands of the Germans.
The Irishmen were held at the Marlag-Milag Nord Prisoner of War camp and were asked to pitch in with the German war effort by working on railways at Bremen and at the shipyards in Hamburg.
But, being from a politically neutral country at the time, they refused to support the Nazis and were swiftly dispatched to the Bremen-Farge concentration camp until their release at the end of the Second World War.
Their accounts speak of “harsh” conditions, food that was “atrocious in quality and quantity” and punishing 12-hour days of hard labour.
In his handwritten letter, Patrick O’Brien, who later lived in Glasgow, said: “Punishment was severe and meted out for the smallest of no demeanour.
“The reason for my imprisonment was my refusal to work on the German railway at Bremen and refusing to work on German ships at Hamburg.
“They claimed I was an Irish national and was therefore a free civilian, a claim which at no time I had ever made.”
His colleague James Aldous Furlong, who was born in Wexford but later moved to Cheshire, told a similar story in his application.
He wrote: “For refusing to work for the Germans I was sent to Farge SS Camp as a punishment and it was punishment place, I have seeing people being flogged to death and shot and was always afraid my turn would come one day (sic).
“Food was bad, accommodation very bad and there was syphilis in the camp and people were dying all over the place.
“However, I came through alright but I am crippled now with rheumatic.”
The men were initially awarded £1,000 in compensation, but were subsequently handed another £1,385.
Each payout prompted a thank-you letter from Mr Furlong – the first saying it would pay “half of the mortgage on my house”, but adding it was “a pity”…