B4

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

Transportation

B4, IATA code of Beond, an airline based in Malé, Maldives
B4, IATA code of B.A.C.H. Flugbetrieb, an Austrian charter airline (ICAO code BCF)
B4, IATA code of Bankair, an US American charter airline (ICAO code BKA)
B4, then-IATA code of Flyglobespan, a former British airline
Auster B.4, 1951 British light transport aircraft with rear ramp
Bensen B-4, Bensen Aircraft autogyro
Bäumer B IV Sausewind, German 1920s sports aircraft
Fokker B.IV, parent company's designation for American branch's F.11 seaplane
Hawker B 4, Swedish designation for Hawker Hart biplane
Keystone B-4, United States biplane bomber
Lohner B.IV, an Austro-Hungarian World War 1 reconnaissance biplane
Pilatus B-4, Swiss glider also designated PC-11.

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, an 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
LB&SCR B4 class, a British tender locomotive class
LNER Class B4, a British class of locomotives

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, "Stalins Hammer"), a World War II Soviet ordnance piece
B-4 a US Air Force/USAAF flight bag
A level of vehicle armour

B4 (music show), a defunct British music video show broadcast on Channel 4
B4 (TV channel), a defunct British music television channel
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
The Lost City (B4), a Dungeons & Dragons adventure module

B4 (classification), a parasports classification for visually impaired athletes
B4 Street Fighter Championships, a 2000 fighting game tournament
B4 or B4 II, a Native Instruments virtual synthesizer for Hammond organ (B-3) sound emulation
B4-mount, used for professional video cameras such as Betacam
An international standard paper size (250×353 mm), defined in ISO 216
B04, Alekhine's Defence chess code
1. b4, Sokolsky Opening in chess