Level 12

Total Experience Required 18,523 [confirmed]

Level 100 progress: 0.27%

This is roughly:
Killing 62 people in Warzone, or...
Killing 64 people in Execution, or...
Killing 53 people in Wingman, or...
Scoring 13,231 points in Guardian, or...
Scoring 40,268 points in Annex, or...
Scoring 24,373 points in Submission.

Horde (TU4)

Completing 93 waves on Casual, or...
Completing 62 waves on Normal, or...
Completing 47 waves on Hardcore, or...
Completing 38 waves on Insane.

Or a combination of the above. Have fun!