| Turkey | the centre of the Ottoman Empire; became a republic in 1923 |
| U-boat | a German submarine |
| ultimatum | a final offer issued in negotiations, the rejection of which can lead to a break in relations and some action |
| undercarriage | the part of a plane, including the wheels, that provides support when it is on the ground and when it is landing or taking off |
| United Kingdom (UK) | refers to the United Kingdom of Great Britain and Ireland from 1 January 1801 to 5 December 1922, or the United Kingdom of Great Britain and Northern Ireland from 5 December 1922 |
| upper class | describes a group of people in a society who have the highest economic or social status |
| vanguard | the part of a military force that goes into battle first; 'van' for short |
| veteran | a person who served in the armed forces of their country during a war or peacekeeping mission |
| Victoria Cross (VC) | the highest decoration for gallantry in the face of the enemy awarded to members of the British and Commonwealth armed forces |
| Viet Cong | a communist guerrilla force that sought to overthrow the South Vietnamese government, later allied with North Vietnam |
| war cry | a rallying cheer or slogan shouted by combatants in battle |
| weight of fire | a measure of the quantity, density and intensity of artillery fire used to attack a target (see also 'fire-effect') |
| White Australia policy | a term for the Immigration Restriction Act 1901 and its amendments, laws that prevented permanent migration of non-European peoples, especially Asians (mostly Chinese) and Pacific Islanders |
| wireless | a telegraphy system that sends messages over a distance by radio signals |