I dont play UT 3 or the others, just the 04, but in 04 (Its proably on the others too,) there is an Assault mode.
Here it goes:
There are two teams, one is defending and one is attacking. The attackers have goals, and they must acomplish them in ten minutes, if they dont, the defenders win. When a goal is acomplished, the players respawn on a new location.
Here is a prewiew (Kinda)
Attackers: Defenders:
1. Infiltrate the main doors. 1. Defend the main doors.
2. Destroy the satelite dish. 2. Defend the satelite dish.
3. Turn off all the three generators. 3. Defend the generators
4. Escape the base. 4. Prevent the attackers to escape the base.
So, there is four goles here, so the round will last for eight minutes.
When the game is over, the attackers become defenders and the defenders become attackers.