The Heinkel He-111 was the mainstay of the German offensive against Great Britain during the “Battle of Britain”. It was produced in far larger quantities than the Do-17 series and remained in service throughout the war. The Heinkel He-111 was first displayed in January 1936, not as a bomber, but in the guise of a civil airliner.
In 1937 the civil disguise of the He-111 was abandoned; He-111 B-1s were sent to the Condor Legion fighting in the Spanish Civil war. The success of the He-111 in Spain played a large part in shaping German bombing policy, which later proved wrong when the lightly armed bombers suffered heavy losses over Britain when opposed by modern and determined fighters. The He-111 H-series was by far the most important variant of the bomber, the H-20 being the first to carry a dorsal gun turret and improved armament together with a redesigned nose and more powerful engines.