| Abbreviation | Definition |
|---|---|
| OBL | OBLigation |
| OBL | Operational BaseLine |
| OBP | Off the Beaten Path |
| OBP | On-Board Processor |
| OBQ | Open Bloody Questions |
| OBRA | Omnibus Budget Reconciliation Act |
| OBS | Observation |
| OBS | OSIS (Ocean Surveillance Information System) Baseline System |
| OBSB | Oahu Base Support Battalion |
| OBST | Obstacle |
| OBSTINTEL | Obstacle Intelligence |
| OBT | Observant |
| OBTC | Officers Basic Training Course |
| OBU | OSIS Baseline Upgrade |
| OBU | Overtaken By Underwear |
| OC | Observer Controller |
| OC | Operations Center |
| OC | Ordnance Corps |
| OC | Other Contingencies |
| OC/T | Observer Controller/ Trainer |