| U | Underfloor | - | Organizations |
| U | Uranium | - | Organizations |
| U-SB | Unified S-Band | - | Organizations |
| U/C | Under Current | - | Organizations |
| U/D | Update | - | Organizations |
| U/L | Uplink (UPLK Preferred) | - | Organizations |
| U/M | Unit Of Measure | - | Organizations |
| U/M | Unmanned | - | Organizations |
| U/M | Unscheduled Maintenance | - | Organizations |
| U/O | Used On | - | Organizations |
| U/V | Under Voltage | - | Organizations |
| U/W | Used With | - | Organizations |
| UA | Microampere | - | Organizations |
| UB | Upper Brace | - | Organizations |
| UB | UpUtility Bridge | - | Organizations |
| UBE | Universal Bus Exercisor | - | Organizations |
| UBIC | Universal Bus Interface Controller | - | Organizations |
| UC | Unsatisfactory Condition | - | Organizations |
| UCC | Universal Checkout Console | - | Organizations |
| UCD | Urine Collection Device | - | Organizations |
| UCN | Uniform Control Number | - | Organizations |
| UCPU | Urine Collection And Pretreatment Unit | - | Organizations |
| UCR | Unsatisfactory Condition Report | - | Organizations |
| UCS | Universal Control System | - | Organizations |
| UCS | UnUtilities Control System | - | Organizations |
| UCTA | Urine Collection Transfer Assembly | - | Organizations |
| UD | Update | - | Organizations |
| UDB | Update Buffer | - | Organizations |
| UDF | Utility And Data Flow | - | Organizations |
| UDL | Updata Link | - | Organizations |
| UDL | Update Link | - | Organizations |
| UDMH | Unsymmetrical Dimethylhydrazine | - | Organizations |
| UDMH/H | Unsymmetrical Dimethylhydrazine Hydrazine Blend | - | Organizations |
| UDOP | Ultrahigh Doppler | - | Organizations |
| UDS | Universal Documentation System | - | Organizations |
| UER | Unique Equipment Register | - | Organizations |
| UF | Microfarad | - | Organizations |
| UFD | User File Directory | - | Organizations |
| UG | Microgram | - | Organizations |
| UHF | Ultrahigh Frequency | - | Organizations |
| UHF | Ultrahigh Frequency | - | Organizations |
| UL | Underload | - | Organizations |
| UL | Unit Of Issue | - | Organizations |
| UL | Uplink | - | Organizations |
| UL | Upper Left (S-Band Antenna) | - | Organizations |
| UL | Upper Limit | - | Organizations |
| UL | User Interface | - | Organizations |
| ULA | Fairbanks | - | Organizations |
| ULL | Ullage | - | Organizations |
| ULO | Unmanned Launch Operations | - | Organizations |
| ULT | Ultimate | - | Organizations |
| UMB | Umbilical | - | Organizations |
| UMBC | Umbilical Cord Cable | - | Organizations |
| UMO | Unmanned Orbital | - | Organizations |
| UMVF | Unmanned Vertical Flight | - | Organizations |
| UNBAL | Unbalance | - | Organizations |
| UNDK | Undock | - | Organizations |
| UNDV | Undervoltage | - | Organizations |
| UNIV | Universal | - | Organizations |
| UNLCH | Unlatch | - | Organizations |
| UNLK | Unlock | - | Organizations |
| UP | Upper | - | Organizations |
| UPLK | Uplink | - | Organizations |
| UPP | User Parameter Processing | - | Organizations |
| UPS | Uninterruptible Power Supply | - | Organizations |
| UPS | Uninterruptible Power System | - | Organizations |
| UPS | Upright Perigee Stage | - | Organizations |
| UPTLM | UPlink Telemetry | - | Organizations |
| UR | Unsatisfactory Report | - | Organizations |
| UR | Upper Right | - | Organizations |
| URA | Urine Receptacle Assembly | - | Organizations |
| URN | Urine | - | Organizations |
| URT | Upright | - | Organizations |
| US | United States | - | Organizations |
| US | Upper Stage | - | Organizations |
| USA | United States Of America | - | Organizations |
| USAF | United States Air Force | - | Organizations |
| USB | Unified S-Band | - | Organizations |
| USB | Upper Side Band | - | Organizations |
| USBE | Unified S-Band Equipment | - | Organizations |
| USBI | United Space Booster | - | Organizations |
| USBS | Unified S-Band System (Subsystem) | - | Organizations |
| USEC | Microsecond | - | Organizations |
| USI | Update Software Identity | - | Organizations |
| USN | United States Navy | - | Organizations |
| USNS | United States Navy Ship | - | Organizations |
| USRA | Universities Space Research Association | - | Organizations |
| USS | United States Ship | - | Organizations |
| USS | United States Standard | - | Organizations |
| USS | Utility Support Structure | - | Organizations |
| UST | United States Testing (Company) | - | Organizations |
| UST | Universal Servicing Tool | - | Organizations |
| UT | Umbilical Tower | - | Organizations |
| UT | Unit Tester | - | Organizations |
| UT | Universal Time | - | Organizations |
| UT&GS | Uplink Text And Graphics System | - | Organizations |
| UTC | Coordinated Universal Time | - | Organizations |
| UTC | Unit Test Cases | - | Organizations |
| UTC | United Technology Center | - | Organizations |
| UTC | Universal Test Console | - | Organizations |
