J.R.R. Tolkien enlisted in the British Army in 1915 during World War I.
Tolkien graduated from Exeter College, Oxford, in 1915 and then joined the Lancashire Fusiliers. He trained as a signals officer and was commissioned as a second lieutenant. His military service placed him in the wider experience of the First World War soon after his university studies.
In 1916, Tolkien was sent to France and took part in the Battle of the Somme. He later contracted trench fever and was returned to England. The loss of several close school friends affected him deeply and became an important part of the personal background often discussed alongside his writing.
It is inaccurate to say that Tolkien fought throughout the entire war. Illness removed him from front-line service, and he spent the remainder of the conflict in Britain in various duties. His wartime experience influenced the atmosphere of some later writing, but specific one-to-one claims about fictional characters should be treated cautiously.