In April 1933, Eoin O'Duffy was given command of the Army Comrades Association (also known as Blueshirts). O'Duffy renamed the movement the National Guard. He also organized marches, flags, salutes ("Hail O'Duffy) based on those in Nazi Germany. This led to fighting in the streets between the National Guard and left-wing groups. In August 1933 the government banned the National Guard from marching to Leinster Lawn.

On the outbreak of the Spanish Civil War O'Duffy began recruiting volunteers to go and fight in the war. Supported by the Catholic Church in Ireland and by right-wing national newspapers, O'Duffy and the first volunteers left travelled from Dublin on 13th November, 1936. It has been argued that the men who went to Spain were mainly motivated by a desire to defend the Catholic Church in Spain.

At the same time, the Irish socialist, Peadar O'Donnell, was urging the formation of volunteer regiments to support the Popular Front government. O'Donnell and Frank Ryan established the Connolly Column (named after James Connolly) and in December 1936, Ryan and eighty volunteers left Dublin for Spain. The majority came from the Free State but there were also a group of socialists from Belfast. Those who went included Charlie Donnelly, Eddie O'Flaherty, Paul Burns, Jackie Hunt, Bill Henry, Eamon McGrotty, Bill Beattie, Paddy McLaughlin, Bill Henry, Peter O'Connor, Peter Power, Johnny Power, Liam Tumilson, Jim Straney, Willie O'Hanlon, Ben Murray and Fred McMahon.

After travelling through southern France by train to Perpignan, they went to the training at Albercete in Spain run by André Marty. The Connolly Column suffered heavy losses at Jarama (February 1937). Charlie Donnelly, Eamon McGrotty, Bill Henry, Liam Tumilson and Bill Beattie were all killed during this battle. Ryan was badly wounded at Jarama in February 1937 and returned to Ireland to recuperate. On his returned to Spain and was appointed adjutant to General José Miaja. Ryan was captured during the Aragón offensive on 1st April, 1938 and was held at the Miranda del Ebro detention camp. He was sentenced to death but after representations from Eamon de Valera his sentence was commuted to thirty years.

Around 1,000 people from Ireland fought in Spanish Civil War. Figures suggest that 750 people joined the Blueshirts and 277 fought with the International Brigades.