Which battle did J.R.R. Tolkien experience during the First World War before becoming seriously ill?

J.R.R. Tolkien experienced the Battle of the Somme during the First World War before becoming seriously ill.

Tolkien served as a second lieutenant in the Lancashire Fusiliers. In 1916, he took part in the Battle of the Somme, one of the largest and bloodiest campaigns of the war. He served as a signals officer, a role involving communication between units under extremely dangerous conditions.

Tolkien developed trench fever later in 1916 and was sent back to England for treatment. The illness prevented his return to the front, and he spent much of the remainder of the war performing home-service duties. The experience of losing close friends and witnessing industrialized warfare remained an important part of his biography.

Readers often claim that individual scenes in Middle-earth directly represent specific battles, but Tolkien resisted simple one-to-one allegorical interpretations. His wartime experience nevertheless informed the emotional seriousness of his writing, including its treatment of courage, friendship, loss, and the destructive effects of war.