- George Oakley
- William O'Brian
- William O'brian
- Patrick O'brien
- John O'brien
- Hugh O'brien
- James O'brien
- Joseph O'Connor
- John McConville O'Connor
- Charles O'connor
- John O'donnal
- J O'donnel
- John O'donnell
- John O'donnell
- Patrick O'Donnell
- William O'donnell
- John O'donnell
- Joseph O'donnell
- John O'donnell
- Francis O'donnell
- John O'donnell
- H O'donnell
- Francis O'donnell
- James O'donnell
- John Odonnell
- J O'donnell
- J O'donoghue
- Charles Armour Oetegenn
- Thomas Kirkwood Oetegenn
- William Ogg
- Robert Bennett Ogg
- Allan James Ogilvie
- Charlie O'hagan
- John O'hagen
- Michael McKearney O'Hara
- Thomas O'hara
- James O'Hara
- Henry Eyre O'Hara
- Henry O'Hare
- James O'Leary
- Stewart Dawson Oliver
- Stewart Dawson Oliver
- Gilbert Oliver
- Harry Oliver
- Olaf Olsen
- Patrick O'malley
- James O'malley
- Joseph O'malley
- Daniel O'neil
- Thomas O'Neill
- Thomas O'neill
- William O'neill
- Patrick O'neill
- Patrick O'neill
- Hugh O'neill
- E O'neill
- Joseph O'neill
- P O'neill
- James Orcheson
- Neil Oribine
- Alexander Oribine
- Joseph Oribine
- William Orkney
- Thomas Bell Orkney
- Robert Orkney
- Edward O'rourke
- John Blair Orr
- Thomas Orr
- William Orr
- William Orr
- John Orr
- Patrick Orr
- Arthur Hargreaves Orr
- James Orr
- David Orr
- Donald Orr
- James Orr
- Alex Orr
- Alexander Orribine
- Samuel Owen
- James Owens
- Samuel Owens
- Martin Owens
- Harry William Warren Owers
Remembering those who fought in the Great War.
