O9 or O-9 may refer to:
, an O-class submarine of the United States Navy O-9, the pay grade for the following senior officer ranks in the U.S. uniformed services: Lieutenant General in the Army, Marine Corps, Air Force, and Space Force Vice Admiral in the Navy, Coast Guard, Public Health Service Commissioned Corps, and NOAA Commissioned Officer Corps Douglas O-9, a variant of the Douglas O-2, a 1920s American observation aircraft O9 (model railways), a narrow-gauge model railway scale Oregon-IX (OIX), an internet exchange; see List of Internet exchange points
See also
09 (disambiguation) 9O (disambiguation) oix (disambiguation)