""Get to cover!"" -Davis
Davis is a member of the mustangs in 'To the summit' missions. He helps out with the opening crossfire and is seen at other points. It is unknown what actually happens to him, however it says at the loading screen for the mission 'Great escape Pt.1' that "All the members of Mustang squad were either captured or killed." Considering there was no attempt to rescue him by Downs or Newman or that he's not seen being detained at any point, it's safe to say that he was one of the ones killed, meaning Downs and Newman are the last remaining mustangs.