O4 may refer to: *

LNER Class O4 The London and North Eastern Railway (LNER) Class O4 initially consisted of the 131 ex-Great Central Railway (GCR) Class 8K 2-8-0 steam locomotives acquired on grouping in 1923. The engines were designed by John G. Robinson and built at the GCR' ...

, a class of ex-Great Central Railway 2-8-0 steam tender locomotives *

Taff Vale Railway O4 class The Taff Vale Railway O4 class was a class of 0-6-2T steam tank locomotives designed by Tom Hurry Riches and introduced to the Taff Vale Railway in 1907. They were rebuilt with taper boilers and superheaters by the Great Western Railway (GWR) ...

, a class of 0-6-2T steam tank locomotives * USS ''O-4'' (SS-65), a 1917 United States O class submarine * O-4, the

pay grade A pay grade is a unit in systems of monetary compensation for employment. It is commonly used in public service, both civil and military, but also for companies of the private sector. Pay grades facilitate the employment process by providing a fix ...

for the following officer ranks in the U.S. uniformed services: **

Major Major (commandant in certain jurisdictions) is a military rank of commissioned officer status, with corresponding ranks existing in many military forces throughout the world. When used unhyphenated and in conjunction with no other indicators ...

in the Army, Marine Corps, Air Force, and Space Force **

Lieutenant Commander Lieutenant commander (also hyphenated lieutenant-commander and abbreviated Lt Cdr, LtCdr. or LCDR) is a commissioned officer rank in many navies. The rank is superior to a lieutenant and subordinate to a commander. The corresponding rank i ...

in the Navy, Coast Guard, Public Health Service Commissioned Corps, and NOAA Commissioned Officer Corps *

Tetraoxygen The tetraoxygen molecule (O4), also called oxozone, is an allotrope of oxygen consisting of four oxygen atoms. History Tetraoxygen was first predicted in 1924 by Gilbert N. Lewis, who proposed it as an explanation for the failure of liquid oxyg ...

(O₄), oxozone * a class of stars in the

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

Otoyol 4 Otoyol 4 ( en, Motorway 4), named Anatolian Motorway ( tr, Anadolu Otoyolu) and abbreviated as O-4, is a toll motorway connecting the northwestern Marmara Region to the Central Anatolia Region in Turkey. It runs parallel to the D.100 for more ...

, a highway from Istanbul to Ankara, Turkey *

Martin XO-4 Martin may refer to: Places * Martin City (disambiguation) * Martin County (disambiguation) * Martin Township (disambiguation) Antarctica * Martin Peninsula, Marie Byrd Land * Port Martin, Adelie Land * Point Martin, South Orkney Islands Austr ...

, an

observation aircraft A surveillance aircraft is an aircraft used for surveillance. They are operated by military forces and other government agencies in roles such as intelligence gathering This is a list of intelligence gathering disciplines. HUMINT Human ...

proposed by the

Glenn L. Martin Company The Glenn L. Martin Company—also known as The Martin Company from 1957-1961—was an American aircraft and aerospace manufacturing company founded by aviation pioneer Glenn L. Martin, and operated between 1917-1961. The Martin Company produc ...

* , the

orthogonal group In mathematics, the orthogonal group in dimension , denoted , is the Group (mathematics), group of isometry, distance-preserving transformations of a Euclidean space of dimension that preserve a fixed point, where the group operation is given by ...

in dimension 4

See also