* 3 kills: Recon Plane - It gives you a radar for 30 seconds.
* 5 kills: Artillery Strike - This is similar to an airstrike in Call of Duty 4, although it concentrates on one place instead of doing a sweep of terrain. Being caught in the vicinity of an artillery strike will also disorient you, even if it is friendly.
* 7 kills: Attack Dogs - This reward summons a pack of attack dogs for your team that will seek out enemy players and attack them for a set time limit. These dogs can be killed with almost any weapon in the game, but they come in a pack and move fast. If the dogs are killed, they will respawn and continue attacking until the time limit runs out. A tactical advantage of the dogs is that you can follow them to find the enemy.

Reference:
http://www.giantbomb.com/call-of-duty-world-at-war/61-20777/