Rank & Skills

SAS: Zombie Assault 2/Insane Asylum
The acheivments are the same for both SAS: Zombie Assault 2 and SAS: Zombie Assault 2 Insane Asylum.

Rank 1: Private - The starting rank.

Rank 2: Corporal

In-game description/unlocks: "Red dot sight"

Rank 3: Sergeant

In-game description/unlocks: "Radar Scanner"

Rank 4: Lieutenant

In-game description/unlocks: "Faster reload" - Reload your gun faster.

Rank 5: Captain

In-game description/unlocks: "Badassness" - a major (looks like a double) maximum health boost.

Rank 6: Major

In-game description/unlocks: "High capacity magazines" - Doubles the amount of ammo in your clip.

Rank 7: Colonel

In-game description/unlocks: "Sentry gun engineer" - Doubles the amount of ammo in your sentry guns.

Ranks 8: General

In-game description/unlocks: "Witness the fitness" - Your player moves faster.

SAS: Zombie Assault 3
There are currently 50 ranks in the game, though originally there were only 40 and all come with different emblems and unlocks. Some ranks will unlock weapons which will then be available for purchase, while others unlock you skills to make the game a little bit easier. As players progress through the ranks, there will begin to be more rounds per match and the unlocks will gradually increase in quality until the maximum rank is reached.

Elite Ranks
Elite Ranks are Rank 41-50. Elite Ranks don't use Normal XP to level up, instead it uses Elite XP that you earn in Nightmare Mode or Normal Purge Mode.