O19

O19 or O-19 may refer to:
 * Kneeland Airport, in by Humboldt County, California, United States
 * O 19-class submarine, of the Royal Netherlands Navy
 * HNLMS O 19, a submarine of the Royal Netherlands Navy
 * Oxygen-19, an isotope of oxygen
 * Thomas-Morse O-19, an observation aircraft of the United States Army Air Corps