First flying in 1935 when Germany was banned from building bombers under the Treaty of Versailles, the Heinkel He111 was at first disguised as a fast transport plane. However, its real purpose soon became clear when it was used as a bomber during the Spanish Civil War. The early variants proved to be capable fast bombers with only small numbers being lost to enemy action.
By the start of the Second World War, the He111 had undergone some major changes, resulting in the P model. The engines were now more powerful Daimler Benz DB601 units, and there was an enlarged glass nose section housing the majority of the crew. This afforded them excellent visibility but made them very vulnerable. During the Battle of Britain, the P variant was being phased out, but it continued to serve in some numbers. Against the modern RAF fighters, the He111 now suffered from a lack of speed and defensive armament. Before being switched to night duties the He111 formed the backbone of the Luftwaffe's bomber force but did suffer some heavy casualties.