| O'Hara | James C | | Sergeant | Source: Nominal roll in WO127 |
| O'Leary | J | | Private | Source: Nominal roll in WO127 |
| O'Neil | J | | Private | Source: Nominal roll in WO127 |
| O'Neill | Robert Armstrong | | Lieutenant | Source: Nominal roll in WO127 |
| Oakley | H | | Private | Source: Nominal roll in WO127 |
| Officer | C M | | Major | Source: Nominal roll in WO127 |
| Ohlson | James | 4164 | Trooper | Source: Nominal roll in WO127 |
| Omanney | Henry Travers | | Lieutenant | Source: Nominal roll in WO127 |
| Orkney | J | | Private | Source: Nominal roll in WO127 |
| Orwin | L F | | Private | Source: Nominal roll in WO127 |
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