O Class

O class may refer to:

• O-class battlecruiser, a class of warships planned for the German Navy just prior to the Second World War
• O and P-class destroyer, the first ships built under the United Kingdom's War Emergency Programme destroyers
• O-class submarine, multiple classes of submarines
  • United States O class submarine
  • Odin-class submarine
  • Oberon-class submarine
  • Several early submarine classes of the Royal Netherlands Navy
• Class O stars, the rarest of all main sequence stars
• NZR O class, a locomotive class of New Zealand steam engines built in the United States
• SECR O class, a British 0-6-0 steam locomotive class
• WAGR O Class, Australian 2-8-0 steam locomotive class built in the late 19th century
• NER Class O, a British 0-4-4T steam locomotive class
• Highland Railway O Class, a British class of 2-4-0, later 4-4-0T, steam locomotives built in the late 1870s
• Steam locomotive O, an early type of Russian steam locomotive