U-joint (universal joint / universal coupling)
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)
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 cover of the Consulate General
Under Secretary of Defense for Acquisition, Technology, and Logistics (USD AT&L)