Level 40

Total Experience Required 302,351

Level 100 progress: 4.43%

This is roughly the same as:

Killing 504 people in Warzone, or...
Killing 515 people in Execution, or...
Killing 428 people in Wingman, or...
Scoring 107,983 points in Guardian, or...
Scoring 328,643 points in Annex, or...
Scoring 198,916 points in Submission.

Horde (TU4)

Completing 756 waves on Casual, or...
Completing 504 waves on Normal, or...
Completing 378 waves on Hardcore, or...
Completing 303 waves on Insane.

Or a combination of the above. Have fun!