Aux air doors.
My sq lost one in '78 at Bergstrom AFB, TX. The centerline tank was not leak checked properly after being hung. After takeoff the fuel was sucked into the aux air door and ignited with a 40' flame behind it. The a/c was IMC over downtown Austin but managed to turn away from town and the crew successfully ejected.
They said the scariest part of the ordeal was the helicopter ride back to the base in marginally VFR weather.