Lewis studied hard and was determined to earn a place at Oxford University. Traveling to the city to take the entrance exam, he was stunned by the beauty of the medieval buildings. However, he returned to Ireland convinced that he had failed the mathematics test. When he received a letter congratulating him on his acceptance, Lewis realized that the university was short of students, as many young men were already fighting in World War I.

When Lewis saw his luxurious college room, the porter explained that the previous resident was fighting in France. Feeling guilty, Lewis enlisted in the British Army, although as an Irishman, he was not compelled to do so. He joined the Officer’s Training Corps while simultaneously studying at Oxford. During training, Lewis shared a room with Paddy Moore, and they became close friends. The young men promised each other that if one of them was killed in combat, the other would take care of their friend’s family.

Lewis believed that it was unlikely that he would be sent to France. However, by his 19th birthday, he was on the frontlines in the Battle of the Somme. Falling ill with trench fever, he was sent to a hospital for five months to recuperate.