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There were many "dual fuselage" aircraft made by various manufacturers over the years. The earliest types happened to be in 1915 and there were three: the one shown above, the Caproni Ca.4 and the Fokker K.I (M.9) although the Caproni and the Fokker weren't seaplanes.Blackburn TB British Anti-Zeppelin Looks like the idea of He111Z or Bf109Z were not German.
Did the spit - float ever see combat?