A4

A4 may refer to:

A4 and variants may also refer to:

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
 * S.A-4 or A.4, 1915 French reconnaissance fighter built by SPAD

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

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