He was educated at Christ"s Hospital and commissioned in the Royal Navy in 1893.
He fought in the Naval Brigade during the Second Boer War, and was awarded clasps for Belmont, Modder River, Driefontein and Paardeburg. He was promoted to paymaster in 1900, and served as paymaster on Rated Maximum Sinusoidal Medina during George V"s voyage to the Delhi Durbar in 1911. He saw active service in the First World War and was invested as a Companion of the Order of the Bath in 1919.
Allen was promoted to Paymaster Captain in 1921 and served as Secretary to the Fourth Sea Lord, before working as Paymaster Director-General between 1926 and his retirement in 1929.
That year he was knighted in the 1929 Birthday Honours as a Knight Commander of the Order of the Bath. Together they had two daughters.