Which military unit did J.R.R. Tolkien serve with during World War I?

During World War I, J.R.R. Tolkien served with the Lancashire Fusiliers.

Tolkien received a commission as a second lieutenant in the British Army in 1915. He trained with the 13th Battalion, Lancashire Fusiliers, before being sent to France in 1916. He served as a signals officer during the Battle of the Somme and became ill with trench fever later that year.

Tolkien’s wartime experience is frequently discussed in relation to his fiction, but it is too simplistic to treat particular characters or events as direct one-to-one allegories of the war. His memories of friendship, loss, ruined landscapes, and industrialized conflict contributed to the emotional and historical depth of his writing. Several close friends from his school days were killed in the war, a fact that deeply affected him.