- OC
- Abbreviation:Officer Commanding
- ONUCA
- Acronym:United Nations Observer Group in Central America
- ONUSAL
- Acronym:United Nations Observer Mission in El Salvador
United Nations Observer Mission in El Salvador
- OP
- Acronym:Observation Post
- OSCE
- Acronym:Operation for Security and Co-Operation in Europe
Operation for Security and Co-Operation in Europe
- OSGA
- Acronym:Office of the Secretary General in Afghanistan
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