Reach Wave 15 in each mission of Special Ops Survival mode.
There's a total of 16 Survival maps you'll need to play here. To make it a little easier, these are best done with one other player. You may also want to note that not all of the maps are available from the start. Some require you to be a certain level within the Survival mode. By simply playing the other maps, you should have no trouble reaching these ranks. All you need to do is reach the 15th wave for it to count, there is no need to complete it.
Please note, that when you reach the 15th wave you MUST die and NOT quit. Quitting out will not register your current wave.
Level 0: Easy
Level 8: Regular
Level 15: Hardened
Level 25: Veteran