Unlock the following bonuses by reaching the corresponding multi-player levels:

BONUS - MULTI-PLAYER LEVEL
3x Frag (Perk Slot 1) - Level 41
AK-47U - Level 28
Bandolier (Perk Slot 1) - Level 32
Barret .50 Cal - Level 49
Bomb Squad (Perk Slot 1) - Level 14
Boot Camp Challenges 1 - Level 09
Boot Camp Challenges 2 - Level 15
Boot Camp Challenges 3 - Level 18
Clan Tag - Level 12
Claymores - Level 23
Create-a-Class - Level 04
Dead Silence (Perk Slot 3) - Level 44
Demolitions Class - Level 02
Desert Eagle - Level 43
Double Tap (Perk Slot 2) - Level 29
Dragunov - Level 22
Eavesdrop (Perk Slot 3) - Level 35
Elite Challenges - Level 51
Elite Challenges 2 - Level 53
Elite Challenges 3 - Level 54
G3 - Level 25
G36C - Level 37
Golden Desert Eagle - Level 55
Gun Challenges - Level 05
Humiliation Challenges 1 - Level 42
Humiliation Challenges 2 - Level 45
Humiliation Challenges 3 - Level 47
Humiliation Challenges 4 - Level 48
Humiliation Challenges 5 - Level 50
Iron Lungs (Perk Slot 3) - Level 26
Killer Challenges 1 - Level 30
Killer Challenges 2 - Level 33
Killer Challenges 3 - Level 36
Killer Challenges 4 - Level 39
Last Stand (Perk Slot 3) - Level 08
M1014 - Level 31
M14 - Level 46
M1911 - Level 16
M21 - Level 07
M4 Carbine - Level 10
M60E4 - Level 19
Martyrdom - Level 17
Mini-Uzi - Level 13
MP44 - Level 52
New Playlists - Level 06
Operations Challenges 1 - Level 21
Operations Challenges 2 - Level 24
Operations Challenges 3 - Level 27
Overkill (Perk Slot 2) - Level 38
P90 - Level 40
Prestige Mode - Level 55
R700 - Level 34
Sleight of Hand (Perk Slot 2) - Level 20
Sniper Class - Level 03
UAV Jammer (Perk Slot 2) - Level 11

Kill streak bonuses:
During online multi-player mode you can call in an air-strike if you get a five kill streak without dying and a helicopter after a seven kill streak. You can call in the airstrike or helicopter at any time in the match, even if you die, as long as you acquired the necessary number of kills without dying. However, there is problem if you get a five kill streak and get two more without dying that allows you to call in a chopper. If you get a seven kill streak and have not used your airstrike, you will not be able to use it. You will be able to use the chopper in the same way. Basically you can get the ability to call in a chopper or airstrike and use it whenever desired, even in the finalminute of the game. This trick also works to call in a UAV after a three kill streak.