A4

A4 most often refers to:

• Audi A4, a luxury compact executive car manufactured by Audi, introduced in 1994
• A4 paper, a paper size defined by the ISO 216 standard, measuring 210 × 297 mm

A4 and variants may also refer to:

Science and mathematics

• British NVC community A4 (Hydrocharis morsus-ranae - Stratiotes aloides community), one type of Aquatic communities in the British National Vegetation Classification system
• Combretastatin A-4, a stilbenoid chemical compound
• A₄, the alternating group on four elements
• A4, a type of stainless steel, as defined by ISO 3506, equivalent to SAE steel grade 316L
• Subfamily A4, a rhodopsin-like receptors subfamily

Medicine

• ATC code A04 Antiemetics and antinauseants, a subgroup of the Anatomical Therapeutic Chemical Classification System
• Lipoxin A4, a lipoxin

Transportation

Aeronautics and astronautics

• "A-4 Helldiver", the civil version of the Curtiss Falcon an attack aircraft manufactured by Curtiss Aircraft Company
• A-4 Skyhawk, a 1954 attack aircraft manufactured by Douglas Aircraft Company
• Breda A.4, a 1926 Italian biplane trainer aircraft
• Aggregat-4, the technical name for V-2 ballistic missile
• A4, Southern Winds Airlines, the defunct Argentine airline, as its IATA code
• A-004, the sixth and final abort test of the Apollo spacecraft
• S.A-4 or A.4, 1915 French reconnaissance fighter built by SPAD

Railways

Locomotives

• Bavarian A IV, an 1852 German steam locomotive model
• LNER Class A4, a class of steam locomotives, including the famous Mallard
• PRR A4, an American Pennsylvania Railroad locomotice classification

Stations

• Togoshi Station, number A-04 on the Toei Asakusa Line

Ships

• A-4, USS Moccasin (SS-5), a Plunger-class submarine of the United States Navy, which was renamed A-4 on 17 November 1911
• HMNZS Kahu (A04), a 1978 Royal New Zealand Navy Moa class inshore patrol vessel
• HMS A4, an A-class submarine of the Royal Navy
• Belgian ship A4, a Belgian naval patrol vessel of World War II

Other vehicles

• Arrows A4, a 1982 British racing car
• Prussian A 4, a 1913 German railbus

Roads and routes

• List of A4 roads
• A4, a Metrobus route in Washington, D.C.

Military

• A4, the model number of the World War II-era German V-2 rocket
• A4, the designation for air force headquarters in the NATO continental staff system concerned with logistics
  • In the United Kingdom, the A4 Air Logistics branch of the Joint Force Air Component Headquarters
• A 4, see List of Swedish regiments for A4, a Swedish designation (4th Artillery Regiment) that has been used by:
  • Gotlands artilleriregemente (unknown–1892)
  • Norrlands artilleriregemente (1893–1997)
• Douglas A-4 Skyhawk, an American attack aircraft introduced in 1956
• M16A4, a variant of the American M16 rifle
• Leopard 1A4, a variant of the German Leopard 1 main battle tank
• Leopard 2A4, a variant of the German Leopard 2 main battle tank

Computing

• Apple A4, a microprocessor used in some Apple products
• AMD A4, a microprocessor

Other uses

• A4 or A₄, the musical note La or A in the fourth octave
• A440 (pitch standard), the use of the musical note A to reference musical pitch
• A04, Encyclopaedia of Chess Openings code for Réti Opening
• A4, a grade (climbing)
• A4, the code for permission to use specific land or premises for pubs and bars in town and country planning in the UK
• A4 Pod, a family of killer whales living in British Columbia coastal waters
• A4, a 1981 component for the Scourge of the Slave Lord adventure in the Dungeons and Dragons role playing game
• Biu-Mandara A.4 languages, a family of languages spoken in Cameroon and Nigeria

See also

• 4A (disambiguation)
• A4A (disambiguation)
• AIV (disambiguation)