The V2 (German: Vergeltungswaffe 2, lit.?'Vengeance Weapon 2'), with the technical name Aggregat 4 (A4), was the world's first long-range guided ballistic missile. The missile, powered by a liquid-propellant rocket engine, was developed during the Second World War in Nazi Germany as a "vengeance weapon" and assigned to attack Allied cities as retaliation for the Allied bombings of German cities. The V2 rocket also became the first artificial object to travel into space by crossing the Kármán line (edge of space) with the vertical launch of MW 18014 on 20 June 1944.

Research of military use of long-range rockets began when the graduate studies of Wernher von Braun were noticed by the German Army. A series of prototypes culminated in the A4, which went to war as the V2. Beginning in September 1944, more than 3,000 V2s were launched by the Wehrmacht against Allied targets, first London and later Antwerp and Liège. According to a 2011 BBC documentary, the attacks from V-2s resulted in the deaths of an estimated 9,000 civilians and military personnel, while a further 12,000 laborers and concentration camp prisoners died as a result of their forced participation in the production of the weapons.

The rockets travelled at supersonic speeds, impacted without audible warning, and proved unstoppable. No effective defense existed. Teams from the Allied forces—the United States, the United Kingdom, France and the Soviet Union—raced to seize major German manufacturing facilities, procure the Germans' missile technology, and capture the V-2s' launching sites. Von Braun and more than 100 core R&D V-2 personnel surrendered to the Americans, and many of the original V-2 team transferred their work to the Redstone Arsenal, where they were relocated as part of Operation Paperclip. The US also captured enough V-2 hardware to build approximately 80 of the missiles. The Soviets gained possession of the V-2 manufacturing facilities after the war, re-established V-2 production, and moved it to the Soviet Union.

At the time, many Germans were interested in American physicist Robert H. Goddard's research. Before 1939, German engineers and scientists occasionally contacted Goddard directly with technical questions. Von Braun used Goddard's plans from various journals and incorporated them into the building of the Aggregate (A) series of rockets, named for the German word for mechanism or mechanical system.