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
This disambiguation page lists articles associated with the same title formed as a letter–number combination.
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