U
U-joint (universal joint / universal coupling)
U.S. Aids to Navigation System
UBACS / Under Body Armour Combat Shirt
UGL pouch (UGL / Underslung Grenade Launcher)
UHF-band (ultrahigh frequency)
UHF radio receiver transmitter (RRT)
uhlan (lance; lancer; lances; ulan)
Ukraine Defence Contact Group (UCG)
UKUSA (The United Kingdom – United States of America Agreement)
ultimate destination (final destination)
UN Commission on Sustainable Development
UN Framework Convention on Climate Change (UNFCCC)
UN-led International Police Task Force
unclassified (security classification)
Uncrewed Air(craft) / Aerial System (UAS)
undeclared member of the intelligence or counter-intelligence agencies
under armor auxiliary power unit (UAAPU)
under barrel grenade launcher (UBGL)
under cover of civilian research
Under Secretary of Defense for Acquisition, Technology, and Logistics (USD AT&L)
Under Secretary of Defense for Intelligence USD(I)
Under Secretary of Defense (USD)
under suspicion of posing a threat to democracy
under-vehicle improvised explosive device (UVIED)
under-wing probe-and-drogue tanking pod
undercover international apparatus