I think it would add a lot of immersion if there were some sort of long-term ranks to achieve, similar to other online shooter games.
Something like:
Airman- 0 kills
Airman First Class- 5 kills
Senior Airman- 15 kills
Staff Sergeant- 30 kills
Technical Sergeant- 50 kills
Master Sergeant- 75 kills
Senior Master Sergeant- 105 kills
Chief Master Sergeant- 140 kills
Second Lieutenant- 190 kills
First Lieutenant- 250 kills
Captain- 320 kills
Major- 400 kills
Lieutenant Colonel- 490 kills
Colonel- 600 kills
You could then display on the player tags. Thoughts?