| Acronyms | Meaning / Significance |
Source |
| UA | User Agent | ITU-T recommendation X.400 |
| UA | User Area | |
| UAC | Upper Area Control Center | |
| UAV | unmanned air vehivle | |
| UAV | unmanned airial vehicle | |
| UCI | unite de compte internalional | |
| UD | user domain | |
| UDP | user data protocol | STC CSNI final report 22/9/95 |
| UDP | user datagram protocol | |
| UFO | UHF follow-on programme | |
| UFV | user field verification | ACCIS |
| UHF | Ultra High Frequency | |
| UI | UNIX international | |
| UIC | Unit Identification Code | |
| UIDL | user interface definition language | |
| UIMS | user interface management system | |
| UISRM | user interface system reference model | |
| UKADGE | United Kingdom Air Defence Ground Environment | |
| ULA | Upper Layer Architecture | |
| ULC | US Liaison Cell | |
| UMA | unmanned aircraft | |
| UMO | Unconventional Military Operation | |
| UMP | universal modem programme | |
| UMS | Universal Modem System | |
| UMTS | universal mobile telecommunications system | |
| UN | United Nations | |
| UNCTAD | UN Conference on Trade and Development | |
| UNESCO | UN Educational, Scientific and Cultural Organisation | |
| UNHCR | UN High Commission for Refugees | |
| UNITER | part of RAFFTS with switching and bulk encrypted 2MB links | |
| UNOCHA | UN Office for the Coordination of Humanitarian Affairs | |
| UNPROFOR | UN Protection Force | |
| UNSC | UN Security Council | |
| UPS | Uninterruptable Power Supply | |
| US TACS | US Theater Air Control System | |
| USA | United States of America | |
| USD | User Service Division | |
| USSP | US special programme | financial compensation |
| UTM | Universal Trans Mercator | |
| UTP | Unshielded Twisted Pair cable | |
| UWS | Universal Workstation |