Heinkel He-111

The Heinkel He-111 was a primary German medium bomber used extensively throughout the European Theatre in World War II (1939–1945) by the Luftwaffe, with major roles in the Battle of Britain, the Blitz on London, and the Eastern Front. It served in nearly all major campaigns, including the invasions of Poland and France, North Africa, and as a torpedo bomber in the Atlantic. 
 
Key Theatres and Operational Use:
European Theatre (WWII): The mainstay of the Luftwaffe bomber force, it was used for strategic bombing, night attacks, and, as the war progressed, maritime operations (torpedo bombing, laying mines).
Spanish Civil War: Used early on by the Condor Legion to test tactics.
Major Campaigns: Played a major role in the Polish campaign, the Battle of France, the Battle of Britain (1940), and the Blitz on London.
Eastern Front & North Africa: Used extensively for bombing and as a transport aircraft later in the war.
Other Operations: Used as a platform to launch V1 flying bombs. 
Export and Other Operators:
Spain: Used by the Spanish Air Force and produced under license as the CASA 2.111, remaining in service until 1973.
Other Nations: Operated by Hungary, Bulgaria, Romania, and Slovakia (Axis allies), as well as China and Turkey before the war. 
 
Despite becoming obsolete, its versatility kept it in operation until 1945, often serving as a transport aircraft in the final stages of the war.