| Regimental number | 503 |
| Place of birth | Chestport, Buller District, New Zealand |
| Place of birth | Westport, New Zealand |
| School | Chestport District High School, Chestport, New Zealand |
| Religion | Church of England |
| Occupation | Amalgamator |
| Address | Hare Street, Kalgoorlie, Western Australia |
| Marital status | Single |
| Age at embarkation | 25 |
| Next of kin | Father, Mr J P Hallahan, Hare Street, Kalgoorlie, Western Australia |
| Previous military service | Seven years Volunteer Service with Goldfield Infantry Regiment |
| Enlistment date | |
| Date of enlistment from Nominal Roll | |
| Rank on enlistment | Sergeant |
| Unit name | 11th Battalion, Machine Gun Section |
| Embarkation details | Unit embarked from Fremantle, Western Australia, on board HMAT A11 Ascanius on |
| Rank from Nominal Roll | 2nd Lieutenant |
| Unit from Nominal Roll | 11th Battalion |
| Recommendations (Medals and Awards) |
Military Medal Refers April-August 1915. Mention in Despatches awarded, and promulgated, 'London Gazette', Supplement, No. 29455 (28 January 1916); 'Commonwealth Gazette' No. 44 (6 April 1916). Recommendation date: Mention in Despatches Awarded, and promulgated, 'London Gazette', third Supplement, No.29522 (27 March 1916); 'Commonwealth Gazette' No. 79 (6 July 1916). |
| Other details from Roll of Honour Circular | '1st Prize winner Randwick School (1912). M.G. Section. Keen student of Machine Gun tactics.' Details from Father. |
| Fate | Killed in Action |
| Place of death or wounding | Peronne, France |
| Age at death | 29 |
| Age at death from cemetery records | 29 |
| Place of burial | Tincourt New British Cemetery (Plot V, Row E, Grave No. 6), France |
| Panel number, Roll of Honour, Australian War Memorial | 62 |
| Miscellaneous information from cemetery records | Parents: James and Janet HALLAHAN, 178 Hare Street, Kalgoorlie, Western Australia |
| Medals |
Military Medal Source: 'Commonwealth Gazette' No. 62 Date: Military Cross Source: 'Commonwealth Gazette' No. 103 Date: |
| Family/military connections | Brothers: Corporal W.A. HALLAHAN, 11th Bn, killed in action, June, 1916; Pte W.J. HALLAHAN, 6th Bn, killed in action, August 1916. |
| Other details |
War service: Western Front Medals: Military Cross, British War Medal, Victory Medal |