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Airdrop a placeable automated Sentry gun

The sentry gun will be unlocked after getting 5 kills in a row or 4 with "Hardline". The sentry gun is dropped through an airdrop similar to the care-package. The player will have to retrieve it from the package which can be tricky if the spawns have changed and you have been killed before capturing your own Sentry Gun airdrop.
The sentry gun is an unmanned weapon capable of automatically acquiring and defeating enemy targets. The Sentry Gun is most effective when placed in a bunker or next to a door, as any enemy trying to escape or enter the tunnel will be killed instantly. The Sentry Gun can easily be destroyed by someone running behind it and knifing it so it's advised that you plant a claymore behind it so it's defend from both angles. The number one weakness of the Sentry Gun is that is can't detect enemy's using "Cold-Blooded", so they can easily walk up to the turret and knife it giving themselves 100XP.

Strategy

The Sentry Gun is a great killstreak for either guarding you back whilst sniping or watching an objective based game such as in Capture the Flag or Domination. The Sentry gun will stick around for a while and there is an added advantage of being able to move it. If one spot has more enemies than the current spot you can simply pick it up and move it. It's very good as guarding the tunnel on for example Wasteland and also general doorways of the maps on Modern Warfare 2 however it is suspect to being knifed.

https://callofduty.wikia.com/wiki/Call_of_Duty_Wiki

Also, run around with it, you see a guy, place it and let it do it's job. Repeat over and over for fun kills.

I put it up on the rock on afgan then switch to a danger close c4 and stick it on it when someone comes ooooo =D