Level 21

Total Experience Required 55,277

Level 100 progress: 0.81%

This is roughly the same as:

Killing 93 people in Warzone, or...
Killing 95 people in Execution, or...
Killing 79 people in Wingman, or...
Scoring 19,742 points in Guardian, or...
Scoring 60,084 points in Annex, or...
Scoring 36,367 points in Submission.

Horde (TU4)

Completing 139 waves on Casual, or...
Completing 93 waves on Normal, or...
Completing 70 waves on Hardcore, or...
Completing 56 waves on Insane.

Or a combination of the above. Have fun!