But Hartmann had been here before, as a young man in the 1930s, to learn the language. He was accompanied by his own mentor, Professor Ludwig Muhlhausen. When war broke out, the pair returned to Germany where, from 1939 through to the final days of the conflict, Hartmann broadcast Nazi radio propaganda directly to Ireland -- in Irish.
The broadcasts hailed Ireland's great "victory" over the British during the War of Independence. They also claimed that, were Ireland to pledge its allegiance to the German cause, no young Irish people would ever again have to emigrate to find work, and the country would no longer live "in fear of attack" from its former oppressor.
Hartmann never once discussed this aspect of his life with Wigger, nor did he ever exhibit a trace of Nazi beliefs or anti-Semitism. "I believe the Nazi ideology was foreign to him," said Wigger.
There was no question that Muhlhausen was a fervent Nazi. He spent most of his 1930s stay in Donegal, where he was frequently seen using a weight on a string to measure the water depth along the coast. A booklet he compiled, which is held in the Irish military archives, blatantly reveals that Muhlhausen was gathering information for a possible German invasion of Ireland.
But why did Hartmann do what he did? Wigger believed, like so many Germans of his generation, may have been pressured into doing it. "He might have felt there was a gun to his back," ventured Wigger, who has clearly been tormented by the issue.
At one point during this engrossing film, he choked back his emotions while talking about the residual guilt he feels over the Nazi atrocities, even though he was only a small child during the war.
In Connemara, Wigger spoke to a man and his daughter who knew Hartmann in the 60s, but were ignorant of his past.
Would it have made any difference to the people there if they'd known he was a Nazi propagandist? Probably not, came the dispiriting answer.
Professor Gearoid Mac Eoin, who lived for a time in Bonn, heard the broadcasts as a boy and also knew Hartmann. "I could see no evidence of Nazism," he said. "He struck me as a very nice man."
Two-thirds of Irish people would have supported Britain in the war against Germany, said Mac Eoin, although his father, who'd been a 1916 volunteer, wouldn't have been among them. As Wigger himself pointed out, there were still plenty of people of that generation who held to the belief that Hitler "was a great man".
In the end, Wigger found the answers he was looking for -- although not the answers he was hoping for -- in Berlin. Newly unearthed archive information on Hartmann reveals he willingly joined the Nazi Party in 1933, long before doing so would have been advantageous to his survival. It was a matter of choice, not circumstances.
Furthermore, he requested that he be employed in the war effort, specifically in the propaganda division, and actively sought a scholarship to pursue his Irish studies, which were a part of the Nazis' wider racial policy. Wigger seemed crushed by what he'd learned.
Irish viewers, meanwhile, will have been disturbed by some of the things it revealed about this country's ambivalent relationship with that dark time.
glaoch on triu reich HHHHI