He quickly became more interested in social rather than Irish nationalist issues and in 1937 decided to volunteer for the International Brigades, motivated in part by the fact that his friend and IRA veteran Kit Conway[4] had been killed in action in the Battle of Jarama on Doyle’s 21st birthday.

After fighting at Belchite, he was captured at Gandesa by the Italian fascist Corpo Truppe Volontarie in 1938, along with Irish International Brigade leader Frank Ryan.

There he was once brought out to be shot and he was regularly tortured by Spanish fascist guards and interrogated by the Gestapo[8] before being released in a prisoner exchange.

Doyle enlisted in the British merchant navy during World War II before settling in London with his Spanish wife, Lola.

In an interview with The Irish Times, he said: "I thought there was a danger that Ireland would go fascist and that was one of the motivating factors in making up my mind to go to Spain."