Call of Duty – Modern Warfare 3: Unlock Levels in Survival Mode
In Call of Duty: Modern Warfare 3 for the PC, PS3, Wii, and Xbox 360, levels in Survival Mode are unlocked gradually as you progress. The levels you start out with are fairly easy, and of course get more difficult as you go along.
Here are the levels that can be unlocked, and what level you need to reach in order to unlock them.
Tier 1 Levels – Easy difficulty, unlocked from the start
Tier 2 Levels – Regular difficulty, unlocked at level 8
Tier 3 Levels – Hard difficulty, unlocked at level 15
Tier 4 Levels – Insane difficulty, unlocked at level 25