| Abbreviation | Definition |
|---|---|
| UNISYS | United Information Systems |
| UNITAR | United Nations Institute For Training And Research |
| UNOLS | University- National Oceanographic Laboratory System |
| UNOLS | University-National Oceanographic Laboratory System |
| UNU | United Nations University |
| UNWILD | Underwater Survey in Lieu of Drydock |
| UOP | Upper Ocean Processes |
| UOR | Undulating Oceanographic Recorder |
| UPD | Underwater Propulsion Device |
| URAC | Underwater Robotic Arm Control |
| URSI | Union Radio-Scientifique Internationale (International Union of Radio Science) |
| US/GCRP | United States Global Change Research Program |
| USACE | United States Army Corps of Engineers |
| USAF | United States Air Force |
| USBL | Ultra Short Base Line |
| USCG | United States Coast Guard |
| USCGS | United States Coast Guard Station |
| USDA | United States Department of Agriculture |
| USDHHS | United States Department of Health and Human Services |
| USDOT | United States Department of Transportation |