O21

O21 may refer to: O21 (film), a 2014 Pakistani action thriller film Hoopa Airport in Humboldt County, California, United States O 21-class submarine, of the Royal Netherlands Navy HNLMS O 21, a submarine of this class O21 scale, a model railway scale Otoyol 21, a motorway in Turkey Oxygen-21, an isotope of oxygen Thomas-Morse O-21, an observation aircraft of the United States Army Air Corps