During World War I, Roger Casement makes efforts to gain German military aid for the 1916 Easter Rising. His journey on the German submarine SM U-19 comes to an end on April 21, 1916.

In April 1916, Germany offers the Irish 20,000 Mosin–Nagant 1891 rifles, ten machine guns and accompanying ammunition, but no German officers. It is a fraction of the quantity of the arms Casement had hoped for, with no military expertise on offer. The weapons leave Germany bound for Ireland on a German cargo vessel named the SS Libau, disguised as a Norwegian vessel, Aud-Norge.

Casement confides his personal papers to Dr. Charles Curry, with whom he has stayed at Riederau on the Ammersee, before leaving Germany. He departs with Robert Monteith and Sergeant Daniel Beverley (Bailey) of the Irish Brigade in a submarine, initially the SM U-20, which develops engine trouble, and then the SM U-19, shortly after the Aud sails. According to Monteith, Casement believes the Germans are toying with him from the start and providing inadequate aid that will doom a rising to failure. He wants to reach Ireland before the shipment of arms and to convince Eoin MacNeill, who he believes is still in control, to cancel the rising.

Casement sends John McGoey, a recently arrived Irish American, through Denmark to Dublin, ostensibly to advise what military aid is coming from Germany and when, but with Casement’s orders “to get the Heads in Ireland to call off the rising and merely try to land the arms and distribute them.” McGoey does not reach Dublin, nor does his message. His fate is unknown until recently. Evidently abandoning the Irish Nationalist cause, he joins the Royal Navy in 1916, survives the war, and later returns to the United States, where he dies in an accident on a building site in 1925.

About 2:00 a.m. on the morning of April 21, 1916, three days before the rising begins, Robert Monteith, Daniel Bailey (calling himself Beverly), and Casement climb into a small boat for the trip to shore at Banna Strand in Tralee Bay, County Kerry. Their boat, now in the Imperial War Museum in London, capsizes before they reach shore.

Monteith helps an exhausted Casement to safety on shore. Casement is convinced that the Rising cannot be successful without a large number of German troops, and the best he has been able to obtain is one boatload of arms. Suffering from a recurrence of the malaria that had plagued him since his days in the Congo, and too weak to travel, Monteith and Bailey leave Casement at the ruins of McKenna’s Fort, an ancient ring fort in Rahoneen, Ardfert, now renamed Casement’s Fort, and head for Tralee.

About 1:30 p.m., Casement is discovered by two Royal Irish Constabulary (RIC) officers. He nearly talks his way out of being arrested, but a 12-year-old boy at the scene points out a piece of paper Casement had tossed away as the police approach. On that paper is a German code list. He is arrested on charges of high treason, sabotage and espionage against the Crown. He manages to send word to Dublin about the inadequate German assistance.

The Kerry Brigade of the Irish Volunteers might have tried to rescue Casement over the next three days, but its leadership in Dublin holds that not a shot is to be fired in Ireland before the Easter Rising is in train and therefore orders the Brigade to “do nothing.” A subsequent internal inquiry attaches “no blame whatsoever” to the local Volunteers for failing to attempt a rescue. Casement is taken to Brixton Prison and placed under special observation for fear of an attempt of suicide as there is no staff at the Tower of London to guard suicidal cases.

Casement’s trial at bar opens at the Royal Courts of Justice on June 26, 1916, before the Lord Chief Justice (Viscount Reading), Justice Horace Avory, and Justice Thomas Horridge. Refusing to agree to a “guilty but insane” plea, he is subsequently found guilty and sentenced to be hanged. He unsuccessfully appeals against his conviction and death sentence.

On the day of his execution by hanging at Pentonville Prison, August 3, 1916, Casement is received into the Catholic Church at his request. He is attended by two Catholic priests, Dean Timothy Ring and Father James Carey, from the East London parish of SS Mary and Michael. The latter, also known as James McCarroll, says of Casement that he was “a saint … we should be praying to him [Casement] instead of for him.” At the time of his death he is 51 years old.

Casement’s body is buried in quicklime in the prison cemetery at the rear of Pentonville Prison, though his last wish was to be buried at Murlough Bay on the north coast of County Antrim, in present-day Northern Ireland. Finally, in 1965, his remains are repatriated to Ireland. His remains lay in state at the Garrison Church, Arbour Hill (now Arbour Hill Prison) in Dublin for five days, close to the graves of other leaders of the 1916 Easter Rising, although he would not be buried beside them. After a state funeral, the remains are buried with full military honours in the republican plot in Glasnevin Cemetery in Dublin, alongside other Irish republicans and nationalists. The President of Ireland, Éamon de Valera, who is then in his mid-eighties and the last surviving leader of the Easter Rising, attends the ceremony, along with an estimated 30,000 others.