• O’Callaghan, Commander Charles 1
• Official Secrets Act (1920) 1
• Oliver, Rear-Admiral Henry 1
• Operation Felix 1, 2
• Operation Goldeneye 1
• Operation Heartbreak (Cooper) 1
• Operation Husky 1
• Operation Mincemeat 1
• Operation Overthrow 1
• Operation Ruthless 1
• Operation Torch 1
• Operational Intelligence Centre (OIC) 1, 2g
• Oxyrhynchus 1, 2, 3