He was in the 2nd Battalion, 24th Regiment of Foot (later The South Wales Borderers), British Army during the Zulu War when the following deed took place for which he was awarded the Victoria Cross for gallantry in action.

[citation needed] On 22 and 23 January 1879 at Rorke's Drift, Natal, South Africa, Corporal Allen and another man (Frederick Hitch) kept communication with the hospital open, despite being severely wounded.

[citation needed] Allen died of pneumonia in the 1889–1890 flu pandemic on 12 March 1890 at 85 Monnow Street, Monmouth at the age of 46.

His body was buried at Monmouth Cemetery, Monmouthshire, with the cost of the grave and the headstone being provisioned by the South Wales Borderers Regiment.

[3][4] A posthumous charity fund was set up to assist his family, his wife, Sarah Ann and his seven children.