Mezue ahịrịokwu na-esonụ: E nyere Allen ọrụ na 1913 ma sonye na Australian Imperial Force (AIF) na 24 June 1915. Allen banyere ụgbọ mmiri gaa Ijipt na ndị enyemaka maka 13th Battalion n'August. N'ọnwa Machị afọ 1916, e mere ya onyeisi ndị agha ma kenye ya n'òtù ndị agha nke 45. Ọ bịarutere France na 8 June 1916 ma lụọ ọgụ na Agha nke Pozières n'August. Allen nọgidere n'ihu agha na Somme n'afọ 1917 ma duru ndị ya n'agha Messines na June. Onyeisi ya n'agbata nnukwu mfu mere ka Allen nweta ihe nrite nke Distinguished Service Order ma bulie ya n'ọkwa onye isi na July. Ọ gara n'ihu idu ndị mmadụ n'agha, n'agha Dernancourt n'ọnwa Eprel afọ 1918, ma bụrụkwa onye ọrụ ọkaibe ndị ọchịagha, na-ahụ maka ndị agha nke iri anọ na asatọ, na
Agha nke Monument Wood.