Table 5.24 -- EDCS Classifications whose label begins with U
| Label | Definition | Related concepts | Code |
| UNCONTROLLED_AIRSPACE | Any airspace in which air traffic control service is not available. | EC AIRSPACE, EC CONTROLLED_AIRSPACE | 926 |
| UNDERGROUND_BUNKER | An underground facility used by the military either for location of command/control centres or for troop encampment. | EC UNDERGROUND_DWELLING | 927 |
| UNDERGROUND_DWELLING | An underground facility providing living quarters. | EC CLIFF_DWELLING | 928 |
| UNDERGROUND_WATER | Water situated underground but reachable by wells, i.e., phreatic water. | 929 | |
| UNDERMINED_LAND | A tract of land, previously undermined through mining activities, that either has already partly subsided or that is in the process of subsiding. | 930 | |
| UNDERWATER_COMM_DEVICE | A device located in water and used to provide two-way communication between a shore station and a mobile platform, e.g., a transponder. | 931 | |
| UNDERWATER_HAZARD | An underwater object or site, known to be hazardous to surface navigation. | 932 | |
| UNDERWATER_OBJECT | An object on the sea floor or underwater which is not included in a more specific characterization. | EC UNDERWATER_REGION | 933 |
| UNDERWATER_OBJECT_OR_REGION | An object or region on the sea floor or underwater which is not included in a more specific characterization. May be further delineated specifically as EC UNDERWATER_OBJECT or EC UNDERWATER_REGION. | EC UNDERWATER_HAZARD | 934 |
| UNDERWATER_REGION | A region of the sea floor or underwater which is not included in a more specific characterization. | EC UNDERWATER_OBJECT | 935 |
| UNVEGETATED_LAND | A tract or region of land with little (less than 5 percent) or no vegetation. | 936 |