Unlock the following bonuses by getting the corresponding amount of consecutive kills without dying:

BONUS - KILLSTREAK/DESCRIPTION
Spy Plane - 3 kills; shows enemies on the mini-map (free).
RC-XD - 3 kills; remote control car with explosives piloted by killstreak user (1,200 points).
Counter-Spy Plane - 4 kills; temporarily disables enemy's mini-map (1,600 points).
SAM Turret - 4 kills; airdrop a turret that destroys aircraft (1,600 points).
Care Package - 5 kills; airdrop a crate that contains a random killstreak, ammo crate, or special weapon (free).
Napalm Strike - 5 kills; airstrike drops fire over an area of the your choicewhich burns and damages enemies temporarily (2,400 points).
Sentry Gun - 6 kills; airdrops anti-personnel sentry gun (3,200 points).
Mortar Team - 6 kills; user targets three locations to be shelled by mortars (3,200 points).
Attack Helicopter - 7 kills; call in automated attack helicopter to a selected location (free).
Valkyrie Rockets - 7 kills; two remote controlled rockets (4,000 points).
Blackbird - 8 kills; advanced version of the spy plane that indicates enemies onthe map and direction they are facing (4,500 points).
Rolling Thunder - 8 kills; B-52 bomber bombs selected location (4,500 points).
Chopper Gunner - 9 kills; control door-mounted mini-gun from a helicopter thatcircles the map; enemies without the Ghost perk are displayed as reddots (5,000 points).
Attack Dogs - 11 kills; call in a group of attack dogs (6,000 points).
Gunship - 11 kills; pilot a helicopter with rockets and machine guns; helicopter can be destroyed (6,000 points).