- SSU
- Acronym:Service Support Unit
- T.D.
- Acronym:Teachtaí Dála: is a member of Dáil Éireann, the lower house of the Oireachtas (the Irish Parliament)
- T/O
- Abbreviation:Take Off
- UN
- Acronym:United Nations
- UNAMET
- Acronym:United Nations Mission in East Timor
- UNAVEM
- Acronym:United Nations Angola Verification Mission
- UNDOF
- Acronym:United Nations Disengagement Observer Force
- UNGOMAP
- Acronym:United Nations Good Offices Mission in Afghanistan and Pakistan
- UNHCR
- Acronym:United Nations High Commission for Refugees
- UNIFIL
- Acronym:United Nation Interim Force in Lebanon
United Nation Interim Force in Lebanon I and II
- UNIKOM
- Item for:United Nations Iraq-Kuwait Observation Mission
- UNIPOM
- Acronym:United Nations India Pakistan Observation Mission
- UNIT - T
- Abbreviation:United Nations Inspection Teams - Tehran
- UNJCC
- Abbreviation:United Nations Joint staff Co-ordination Center
- UNMEE
- Acronym:United Nations Mission in Ethiopia and Eritrea
- UNMIK
- Acronym:United Nations Interim Administration Mission in Kosovo
- UNMIL
- Acronym:United Nations Mission in Liberia
- UNMO
- Acronym:United Nations Military Observer
- UNMOGIP
- Acronym:United Nations Military Observer Group in India and Pakistan
- UNMOP
- Acronym:United Nations Mission to Prevlaka