The Dornier Do 18 was designed for two roles, to be a medium range maritime reconnaissance aircraft and a mail plane flying boat. It was built to replace the Dornier Wal for the Deutsche Lufthansa. The first prototypes flew during March 1935 then later in 1938 most of the 148 production planes were assigned to military service. The Do 18 had many encounters during the early conflicts between the Kreigsmarine and the Royal Navy, in and around the North Sea.