Level 51

Total Experience Required 669,305

Level 100 progress: 9.81%

This is roughly the same as:

Killing 1,116 people in Warzone, or...
Killing 1,139 people in Execution, or...
Killing 946 people in Wingman, or...
Scoring 239,038 points in Guardian, or...
Scoring 727,506 points in Annex, or...
Scoring 440,333 points in Submission.

Horde (TU4)

Completing 1,674 waves on Casual, or...
Completing 1,116 waves on Normal, or...
Completing 837 waves on Hardcore, or...
Completing 670 waves on Insane.

Or a combination of the above. Have fun!