The AH-6J Little Bird is a helicopter that appears in Spec Ops: The Line. It is used by the 33rd Infantry to attack Delta Squad.
They appear in the campaign during the Intro, Chapter 6 and Chapter 12. They can be shot down using the Minigun in the stolen MH-60L DAP during the Intro and Chapter 12 (as these are technically the same scene), but in Chapter 6 there is no method of eliminating it and so it must be fled from.
It is unknown how many of these choppers the 33rd possess, though the number is at least 9, since 9 were destroyed by Delta through the course of the game. One was destroyed during Chapter 10 - B, and 8 were destroyed during the helicopter chase sequence of Chapter 12. It is possible Freebird was among one of these, but this is unknown.