O class or Class O may refer to:

Rail transport

Highland Railway O Class The Highland Railway O Class locomotives were built as 2-4-0T tank engines, but were soon rebuilt as 4-4-0Ts. They were designed by David Jones for Scottish Railway companies and three were built at the company's Lochgorm Works in 1878 and 18 ...

, a British class of 2-4-0, later 4-4-0T, steam locomotives built in the late 1870s * NER Class O, a British 0-4-4T steam locomotive class * NZR O class, a locomotive class of New Zealand steam engines built in the United States *

Russian locomotive class O The Russian steam locomotive class O (from russian: Основной) was an early type of Russian steam locomotives. 9,129 locomotives were built between 1890 and 1928; hence it was the second most numerous class of locomotive in Russia, after ...

, an early type of Russian steam locomotive *

SER O class The South Eastern Railway (SER) O Class (some of which were later rebuilt, becoming the O1 Class) was a class of 0-6-0 steam locomotive designed for freight work, and were the main freight engines of the SER, and later the South Eastern and Ch ...

, a British 0-6-0 steam locomotive class *

WAGR O class The Western Australian Government Railways (WAGR) O Class was a class consisting of fifty-six 2-8-0 steam locomotives which were introduced by the WAGR between 1896 and 1912. Despite them being tender locomotives, they also featured short boil ...

, Australian 2-8-0 steam locomotive class built in the late 19th century *

O-class Melbourne tram The O-class Melbourne tram were a group of four trams built in 1912 by Duncan & Fraser (Adelaide) for the Prahran & Malvern Tramways Trust (P&MTT) upon the recommendation of W. G. T. Goodman, Chief Engineer and General manager of the Trams in Adel ...

O-class Sydney tram The O-class trams were a class of trams operated on the Trams in Sydney, Sydney tram network. History A prototype (806) was built at Randwick Bus Depot, Randwick Tramway Workshops in 1907, before the Meadowbank Manufacturing Company built a furt ...

Stars

* Class O stars, the rarest of all main sequence stars

Vessels

* , the first ships built under the United Kingdom's War Emergency Programme destroyers * , a class of warships planned for the German Navy just prior to the Second World War *

O-class submarine (disambiguation) O-class submarine may refer to: * * * * Several early submarine classes A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The ter ...

** Class O, several early submarine classes of the Royal Netherlands Navy ** ** **

United States O-class submarine The United States Navy's sixteen O-class submarines were created out of the lessons learned from the L class. The O class were about 80 tons larger than the L class, with greater power and endurance for ocean patrols. Due to the American entry ...

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