X-Ray is the team that was sent to Hue City, Vietnam to extract a defector and his info about the Soviet Union. They appear in "The Defector". X-Ray is made up of Alex Mason and Frank Woods, though Joseph Bowman breaks off from Lima Niner and joins them.
In Hue City, X-Ray flew in on Hotel Six's helicopter. Woods and Mason rappelled down to the building, but Hotel Six was shot down, so they swung on their ropes into a window. X-Ray searches the building, with assistance from Lima Niner, and Bowman and a U.S. Marine rappel from a window, but the Marine is usually killed.
They clear more of the building, and eventually come to a hallway where Mason splits up from the other two. Mason hallucinates his old colleague, Viktor Reznov, and sees him as the defector. Reznov hands Mason a dossier, and fights with X-Ray. X-Ray eventually come back together and move on, and they fight their way to an LZ. Unfortunately, all helicopters are being used to extract wounded soldiers, and X-Ray must defend the LZ. The North Vietnamese Army attack it, and they eventually get so bad that they bring a tank.
Thankfully, a squadron is available for assistance against the NVA, and Woods gets Command to find an evacuation vehicle, a Navy PBR. They jump on it and leave just as the squadron strikes at the NVA.