O21

O21, O 21 or O-21 may refer to:

• O21 (film), a 2014 Pakistani action thriller film
• O21, FAA identifier for Hoopa Airport
• O 21-class submarine, a class of submarines built for the Royal Netherlands Navy
  • HNLMS O 21, a submarine of this class
• O21 scale, a set of model railway standards for narrow gauge railways
• Otoyol 21, a motorway in Turkey
• Thomas-Morse O-21, an American observation biplane

See also

• 021 (disambiguation)