He immediately decided to enlist, partly out of duty, partly because he dreaded the thought of going to Oxford. He joined the Royal Welch Fusiliers at their regimental depot in Wrexham, where he began his military training, and in May 1915 was sent to France. The horrors of trench warfare and the gradual sense of the futility of war are reflected in Robert’s war-poetry. He shared these feelings about the war and about poetry with his fellow poet and close friend, Siegfried Sassoon, also in the Royal Welch Fusiliers.. In May 1916 Robert published his first book of poems, Over the Brazier. In July of that same year, in the battle of the Somme, four days before his 21st birthday, and already a captain, he was so seriously wounded through the lung by shrapnel that his family was told he had “died of wounds”.
After a period of recovery in England, Robert returned to France in January 1917, but his weakened lungs were unable to endure the harsh conditions, even behind the lines. He was sent back home and declared unfit to return to France. It was then he fell in love with seventeen-year-old Nancy Nicholson, whom he had first met in May 1916 when on leave. She was the daughter of the painters William and Mabel Nicholson, the sister of the painter Ben Nicholson and herself an artist and an ardent feminist. They were married at St. James’s, Piccadilly, on January 23rd 1918, by which time the success of his Fairies and Fusiliers (1917) had established Robert as a war-poet. However, war had left him not only with physical scars but with severe shell-shock or war neurosis. In February 1919, shortly after the birth of his first child, Jenny, he was demobilized.