B4

B4, B04, B.IV or B-4 may refer to:

Transportation

Aviation

• Auster B.4, an unusual 1951 British development of the Auster family of light aircraft
• Lohner B.IV, an aircraft
• Bensen B-4, a Bensen Aircraft product
• Flyglobespan IATA airline designator
• B.A.C.H. Flugbetriebs IATA airline designator (ICAO BCF)
• Bankair IATA code, ICAO airline designator (BKA)

Locomotives

• Alsace-Lorraine B 4, an Alsace-Lorraine P 1 class steam locomotive
• Bavarian B IV, an 1852 German steam locomotive
• GSR Class B4, a former Cork, Bandon and South Coast Railway steam locomotive of the Great Southern Railways, Ireland
• LSWR B4 class, a 1891 British dock tank locomotive
• PRR B4, an American Pennsylvania Railroad steam locomotive
• Soo Line B-4 class, an American 0-6-0 steam locomotive

Automotive uses

• Subaru B4, the name under which the Subaru Legacy is marketed in Israel
• B4 (New York City bus), serving Brooklyn
• B4 road (Cyprus)

In the military

• HMS B4, a British B-class submarine of the Royal Navy
• Keystone B-4, a United States Army Air Corps biplane bomber
• SM UB-4, a 1915 German U-boat
• 203-mm howitzer M1931 (B-4), a World War II Soviet ordnance piece

In science

• Leukotriene B4 receptor and Leukotriene B4 receptor 2, two human genes
• Proanthocyanidin B4, a B type proanthocyanidin
• Vitamin B4, an alternate name for adenine
• a stellar classification

In entertainment

• B4 (music show), an early morning pop promo show on Channel 4 TV
• B-4 (Star Trek), an android in the Star Trek fictional universe
• Babylon 4 space station, predecessor to Babylon 5 from the Babylon 5 television series

Other uses

• B4 or B4 II, a Native Instruments virtual synthesizer for Hammond organ (B-3) sound emulation
• B4 lens mount, used for professional video cameras such as Betacam
• an international standard paper size (250×353 mm), defined in ISO 216
• a level of vehicle armour
• B04, Alekhine's Defence chess code
• Flat B4, A4 Froggatt's greatest rivals at The Endcliffe Village in Sheffield.