O4

O4 may refer to:

• SP&S Class O-4, a steam locomotives class
• LNER Class O4, a class of ex Great Central Railway 2-8-0 steam tender locomotives
• USS O-4 (SS-65), a United States O class submarine

• Tetraoxygen (O₄)
• a class of stars in the stellar classification
• Otoyol 4, a Turkish highway from Istanbul to Ankara

See also

• 04 (disambiguation)

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