A4

A4 may mean:

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• A4 paper size, an international standard paper size (210×297 mm) defined by ISO 216
• Audi A4, a brand of car
• HMS A4, an A-class submarine of the Royal Navy
• LNER Class A4, a class of steam locomotives, including the famous Mallard
• Southern Winds, the Argentine airline, as its IATA code
• V-2 rocket, as the actual model number for the German weapon

The variant A-4 may mean:

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• A-4 Skyhawk, an attack aircraft manufactured by Douglas Aircraft Company
• USS Moccasin (SS-5), a Plunger-class submarine of the United States Navy

A4 is the name of several roads:

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• A4 road (England), connecting London to Bristol
• A4 (Switzerland), connecting Schaffhausen to central Switzerland
• A4 (France), a highway connecting Paris to Strasbourg as part of the European routes E50 and E25
• A4 (Italy), a part of the autostrada connecting Torino to Trieste
• A4 (Poland), an incomplete road intended to connect Zgorzelec to Korczowa
• A4 road in Northern Ireland.