O9
# O9

O9 or O-9 may refer to:

* USS O-9 (SS-70), 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)
* Oregon-IX (OIX), an internet exchange; see List of Internet exchange points
