The Ammo Airdrop is a Support killstreak requiring 3 kills. It is unlocked by default.
When deployed, an unarmed MH6 helicopter flies to the target location to drop off the Ammo crate. It contains 3 magazines for both weapons in hand, and 1 equipment charge. It is also the only way to carry 2 equipment items without the use of Bandolier.
It is initially useful, but the Scavenger perk diminishes its utility as the player can simply refill their ammo from dead allies and enemies alike.