Mode II is ONLY used by military.
https://www.aopa.org/training-and-safety/pic-archive/equipment/transponder-requirements
Modes and Codes:
Mode A. Sometimes referred to as mode 3/A. Civil Mode A is identical to military Mode 3. Mode A responds to an ATC interrogation signal with the transponder code set by the pilot.
Edited by Spanky at 13:16:18 on 10/17/17