| O'Brien | John | | Bearer | Served 12 Dec 99 to 12 Mar 00.
Source: Nominal roll in WO127 | Natal Volunteer Ambulance Corps |
| O'Brien | John | | Orderly | Source: Nominal roll in WO127 | Imperial Hospital Corps |
| O'Brien | John | 680 | | Attested: Nov 1898. Source: CMP 41 | Cape Police |
| O'Brien | John | | | Source: Attestation paper in WO126 | Brabant's Horse |
| O'Brien | John | | | 1st Battalion
Source: QSA and KSA medal rolls | Royal Dublin Fusiliers |
| O'Brien | John | 234 | Private | Source: OZ-Boer database | Queensland, 1st Mounted Infantry Contingent |
| O'Brien | John Cahill | 359 | Trumpeter | Source: OZ-Boer database | Queensland, 7th Battalion Australian Commonwealth |
| O'Brien | John Charles William | 289 | Private | Source: Nominal roll in WO127 | Imperial Light Infantry |
| O'Brien | John Charles William | 30501 | Trooper | Source: Nominal roll in WO127 | Prince of Wales Light Horse |
| O'Brien | John Domick | 40262 | Trooper | Source: Nominal roll in WO127 | Kimberley Horse |
| O'Brien | John Emmett | 585 | Trooper | 1st Battalion
Source: Nominal roll in WO127 | Imperial Light Horse |
| O'Brien | John Emmett | | | 1st Battalion
Source: QSA and KSA rolls | Imperial Light Horse |
| O'Brien | John Ernest | 31809 | Private | Source: QSA Medal Rolls | 43rd Company, 12th Btn, IY |
| O'Brien | John James | 39 | | Source: Medal rolls | Canada, 1st Canadian Mounted Rifles |
| O'Brien | John James | 671 | Private | Source: OZ-Boer database | Victoria, 2nd Battalion Australian Commonwealth Ho |
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