Orpen was commissioned into the Army Service Corps as a second lieutenant in March 1916, and worked as a clerk at Kensington Barracks. But under the war artist's scheme, in January 1917 he was released from these duties, given the rank of major, and, in April, arrived in Amiens. Orpen was only the second war artist to be appointed, after Muirhead Bone (1876-1953), and he was employed full time to record the conflict. In the spring and summer of 1917 he painted the battlefields of the Somme, sometimes at places that had been captured only a short time earlier. Orpen described in a letter the shocking experience of seeing numbers of corpses lying unburied among the flooded shell holes, in a landscape totally empty of life. In his pictures of the blasted battlefields, and in his portraits of the exhausted or shell-shocked men, Orpen got physically and emotionally closer to the full horrors of the First World War than most of the other official artists.
Before being presented to the Imperial War Museum, these works were exhibited at Agnew's in London in May 1918, to immense popular acclaim. The public responded positively to the frankness of Orpen's brutal realism, and the exhibition secured Orpen his knighthood. He returned to France in July 1918, and remained there almost constantly until the signing of the Treaty of Versailles in 1919. During this period Orpen began to paint more overtly allegorical compositions about the War and many portraits of the delegates to the Peace Conference. But he also recorded a few further battlefield scenes, like Zonnebeke, made in the style of his pictures of the previous year. Zonnebeke, in Flanders, was the scene of bitter fighting as part of the Passchendaele campaign from June to November 1917. A massive British offensive against enemy installations initially succeeded brilliantly. But prolonged rainfall and heavy shelling transformed the battlefield into a swamp, and the Germans, operating from concrete pillboxes, took a heavy toll of Allied troops with mustard gas and machine-gun fire. At some points at Zonnebeke the Allied and German trenches there were just seven yards apart, and there was terrible loss of life. In a series of attacks and counter-attacks Zonnebeke itself was completely destroyed. When the British finally halted the Passchendaele offensive in November 1917, both sides had each lost 250,000 men, and the Allied lines had advanced just five miles.
Orpen's experience of the War changed him forever. While enormously successful afterwards as portraitist to the British establishment, he remained bitter about the human loss and blamed the politicians and generals for asking the ordinary soldier to make unbearable sacrifices. In 1921 he published an account of his time as a war artist in An Onlooker in France 1917-1919. This contained passages which derided the politicians' cynicism, but was nevertheless hailed by the Daily Express as 'The most frank, unconventional, humorous, tragic human book about the Great War that has been written'.
Sir William Orpen, An Onlooker in France 1917-1919, London 1921
Bruce Arnold, Orpen: Mirror to an Age, London, 1981, pp.308-80