With
Ireland having become embroiled in the Great War Kettle returned to Dublin. On arrival back home he sided with the
National Volunteers in a split within the
Irish Volunteers nationalist militia's ranks between those for whom Irish independence was all, and were increasingly eying the possibility an armed confrontation with the British Government (with the threat of an armed insurrection against Irish Nationalism from Ulster having abated with the
Ulster Volunteers having enlisted en masse into the British Army to fight in World War I), and those who followed
John Redmond's constitutional lead in accepting the
Government of the United Kingdom's public undertaking of a restoration of self-government to Ireland in its domestic affairs, temporarily deferred until the war's end, and who were also concerned about matters beyond Ireland's shores with Europe's future in the 20th Century now being decided. In consequence Kettle volunteered for active service with the 7th Battalion of the
Leinster Regiment, but was refused on the grounds of fragile health. He subsequently received a commission into the
British Army with the rank of
Lieutenant, restricted to garrison service at home. He applied to be an
Irish Parliamentary Party candidate for a by-election in
East Galway, and though not selected his support for the party did not abate, continuing to advocate both home rule and voluntary enlistment with the British Arms, maintaining that Irishmen had a moral duty to join the
allied stand against the displayed tyranny on the European continent of the II Reich. He asserted that "Having broken like an armed burglar into Belgium, Germany was thereby guilty of a systematic campaign of murder, pillage, outrage, and destruction, planned and ordered by her military and intellectual leaders." By 1916 Kettle had published more than ten books and pamphlets, contributed numerous articles to journals and newspapers on Irish politics, literary reviews, poetry and essays, philosophical treatises and translations from German and French. Although at times melancholy at the war's immense escalating intensity across Europe, consuming ever more men and causing destruction to its nations, he continued to apply to be sent to the
Western Front on active service, until, with his health somewhat improved, he received a commission into the 9th Battalion of the
Royal Dublin Fusiliers, amidst the
16th (Irish) Division, which in early 1916 he went to France with, serving alongside
Emmet Dalton, a 19-year-old
subaltern, whose family Kettle had known and frequented the Dublin home of pre-war. The conditions in the trenches of the Western Front broke his health again, and he returned to Dublin shortly after the failure of the abortive
Easter Revolution on sick leave, seeing the wreckage of the city's centre caused by the fighting that had occurred there. He was also beginning to rely too heavily on alcohol in this period as a psychological palliative to the stress of military active service. Whilst in Dublin he rejected offers of a permanent staff position, and returned to rejoin the Battalion in the line. On leaving Ireland on 14 July 1916 he predicted that the Easter Revolutionaries of 1916 would be lionized as patriots in the near future of Ireland's history, whilst those who had fought with the British Arms in World War I would be condemned: "...these men will go down to history as heroes and martyrs and I will go down, if I go down at all as a bloody British officer." Kettle was angered by actions of the Revolutionary faction that had staged the failed revolt, feeling that they were marring Constitutional Nationalism's long worked for strategy of the rebirth of a sovereign Irish state finding its place amidst the nations in a peaceful fashion, with good spirit amidst its neighbours in Britain. It was as an Irish soldier in a war in the defence of European civilisation that he entered the war. He was deeply steeped in Europe's cultures. Kettle's ambition for Ireland in the 20th century was a land and culture with the European continent as its polestar. He wrote: "My only programme for Ireland consists in equal parts of Home Rule and the Ten Commandments. My only counsel to Ireland is, that to become deeply Irish, she must become European"; and later, "Used with the wisdom that is sown in tears and blood, this tragedy of Europe may be and must be the prologue to the two reconciliations of which all statesmen have dreamed, the reconciliation of Protestant Ulster with Ireland, and the reconciliation of Ireland with Great Britain." In a letter, sent to his friend
Joseph Devlin from France shortly before his death, Kettle wrote: "I hope to come back. If not, I believe that to sleep here in the France that I have loved is no harsh fate, and that so passing out into silence, I shall help towards the Irish settlement. Give my love to my colleagues – the Irish people have no need of it." ==Death==