Born in Belford, Allen enlisted in York at the age of 15. His regiment became the South Wales Borderers. He took part in the famous defence of Rorke's Drift in 1879, during the Zulu War, and was awarded the Victoria Cross. He was presented with it by Queen Victoria on 9 December of that year, and the medal is now on display in the regimental museum. The dramatic events at Rorke's Drift were vividly portrayed in the film Zulu, with Michael Caine and Stanley Baker.