Randolph Field flightline showing BT-9s in one of those photos so dearly beloved by the Air Corps, but required the pilots to broil in the Texas sun while the cameraman got things right.
BT-9 at Langley Field, Va.
Popular Aviation, June, 1939.
The BT-14 was a derivative of the BT-9 and is readily identified by its metal fuselage (the BT-9 was mostly fabric covered).